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Chinese Civil War

The Chinese Civil War was fought between the Kuomintang-led government of the Republic of China and the forces of the Chinese Communist Party (CCP), with armed conflict continuing intermittently from 1 August 1927 until 7 December 1949, resulting in a communist victory and control of mainland China.

The war is generally divided into two phases with an interlude: from August 1927 to 1937, the First United Front alliance of the KMT and CCP collapsed during the Northern Expedition, and the Nationalists controlled most of China. From 1937 to 1945, hostilities were mostly put on hold as the Second United Front fought the Japanese invasion of China with eventual help from the Allies of World War II, although armed clashes between the groups remained common. Exacerbating the divisions within China further was the formation of the Wang Jingwei regime, a Japan-sponsored puppet government ostensibly led by Wang Jingwei, which was established to nominally govern the regions of China that came under Japanese occupation.

The civil war resumed as soon as it became apparent that Japanese defeat was imminent, with the communists gaining the upper hand in the second phase of the war from 1945 to 1949, generally referred to as the Chinese Communist Revolution.

The Communists gained control of mainland China and proclaimed the People's Republic of China in 1949, forcing the leadership of the Republic of China to retreat to the island of Taiwan. Starting in the 1950s, a lasting political and military stand-off between the two sides of the Taiwan Strait has ensued, with the ROC in Taiwan and the PRC on the mainland both claiming to be the legitimate government of all China. After the Second Taiwan Strait Crisis, both tacitly ceased to engage in open conflict in 1979; however, no armistice or peace treaty has ever been signed.

Background
Following the collapse of the Qing dynasty and the 1911 Revolution, Sun Yat-sen assumed the presidency of the newly formed Republic of China, and was shortly thereafter succeeded by Yuan Shikai. Yuan was frustrated in a short-lived attempt to restore monarchy in China, and China fell into power struggle after his death in 1916.

The Kuomintang (KMT), led by Sun Yat-sen, created a new government in Guangzhou to rival the warlords who ruled over large swathes of China and prevented the formation of a solid central government. After Sun's efforts to obtain aid from Western countries were ignored, he turned to the Soviet Union. In 1923, Sun and Soviet representative Adolph Joffe in Shanghai pledged Soviet assistance to China's unification in the Sun–Joffe Manifesto, a declaration of cooperation among the Comintern, KMT, and the Chinese Communist Party (CCP). Comintern agent Mikhail Borodin arrived in 1923 to aid in the reorganization and consolidation of both the CCP and the KMT along the lines of the Communist Party of the Soviet Union. The CCP, which was initially a study group, and the KMT jointly formed the First United Front.

In 1923, Sun sent Chiang Kai-shek, one of his lieutenants, for several months of military and political study in Moscow. Chiang then became the head of the Whampoa Military Academy that trained the next generation of military leaders. The Soviets provided the academy with teaching material, organization, and equipment, including munitions. They also provided education in many of the techniques for mass mobilization. With this aid, Sun raised a dedicated "army of the party", with which he hoped to defeat the warlords militarily. CCP members were also present in the academy, and many of them became instructors, including Zhou Enlai, who was made a political instructor.

Communist members were allowed to join the KMT on an individual basis. The CCP itself was still small at the time, having a membership of 300 in 1922 and only 1,500 by 1925. As of 1923, the KMT had 50,000 members.

However, after Sun died in 1925, the KMT split into left- and right-wing movements. KMT members worried that the Soviets were trying to destroy the KMT from inside using the CCP. The CCP then began movements in opposition of the Northern Expedition, passing a resolution against it at a party meeting.

Then, in March 1927, the KMT held its second party meeting where the Soviets helped pass resolutions against the Expedition and curbing Chiang's power. Soon, the KMT would be clearly divided.

Throughout this time, the Soviet Union sent money and spies to support the CCP. Without their support, the CCP likely would have failed. This is evidenced by documents showing other communist parties in China at the time, one with as many as 10,000 members, which all failed without support from the Soviet Union.

Shanghai Massacre and Northern Expedition
In early 1927, the KMT-CCP rivalry led to a split in the revolutionary ranks. The CCP and the left wing of the KMT decided to move the seat of the KMT government from Guangzhou to Wuhan, where communist influence was strong. However, Chiang and Li Zongren, whose armies defeated the warlord Sun Chuanfang, moved eastward toward Jiangxi. The leftists rejected Chiang's demand to eliminate Communist influence within KMT, and Chiang denounced them for betraying Sun Yat-sen's Three Principles of the People by taking orders from the Soviet Union. According to Mao Zedong, Chiang's tolerance of the CCP in the KMT camp decreased as his power increased.

On 7 April, Chiang and several other KMT leaders held a meeting, during which they proposed that Communist activities were socially and economically disruptive and had to be undone for the Nationalist revolution to proceed. On 12 April, in Shanghai, many Communist members in the KMT were purged through hundreds of arrests and executions on the orders of General Bai Chongxi. The CCP referred to this as the 12 April Incident, the White Terror, or the Shanghai Massacre. This incident widened the rift between Chiang and Wang Jingwei, the leader of the left wing faction of the left wing of the KMT also expelled CCP members from the Wuhan government, which in turn was toppled by Chiang Kai-shek. The KMT resumed its campaign against warlords and captured Beijing in June 1928. Soon, most of eastern China was under the control of the Nanjing central government, which received prompt international recognition as the sole legitimate government of China. The KMT government announced, in conformity with Sun Yat-sen, the formula for the three stages of revolution: military unification, political tutelage, and constitutional democracy.

Communist insurgency (1927–1937)
On 1 August 1927, the CCP launched an uprising in Nanchang against the Nationalist government in Wuhan. This conflict led to the creation of the Red Army. On 4 August, the main forces of the Red Army left Nanchang and headed southwards for an assault on Guangdong. Nationalist forces quickly reoccupied Nanchang while the remaining members of the CCP in Nanchang went into hiding. A CCP meeting on 7 August confirmed the objective of the party was to seize the political power by force, but the CCP was quickly suppressed the next day by the Nationalist government in Wuhan, led by Wang Jingwei. On 14 August, Chiang Kai-shek announced his temporary retirement, as the Wuhan faction and Nanjing faction of the Kuomintang were allied once again with common goal of suppressing the CCP after the earlier split. Wang Jingwei took the leadership of KMT after Chiang.

Attempts were later made by the CCP to take the cities of Changsha, Shantou and Guangzhou. The Red Army consisting of mutinous former National Revolutionary Army (NRA) soldiers as well as armed peasants established control over several areas in southern China. KMT forces continued to attempt to suppress the rebellions. Then, in September, Wang Jingwei was forced out of Wuhan. September also saw an unsuccessful armed rural insurrection, known as the Autumn Harvest Uprising, led by Mao Zedong. Borodin then returned to the Soviet Union in October via Mongolia. In November, Chiang Kai-shek went to Shanghai and invited Wang to join him. On 11 December, the CCP started the Guangzhou Uprising, establishing a soviet there the next day, but lost the city by 13 December to a counter-attack under the orders of General Zhang Fakui. On 16 December, Wang Jingwei fled to France. There were now three capitals in China: the internationally recognized republic capital in Beijing, the CCP and left-wing KMT at Wuhan and the right-wing KMT regime at Nanjing, which would remain the KMT capital for the next decade.

This marked the beginning of a ten-year armed struggle, known in mainland China as the "Ten-Year Civil War" (十年内战) which ended with the Xi'an Incident, when Chiang Kai-shek was forced to form the Second United Front against invading forces from the Empire of Japan. In 1930, the Central Plains War broke out as an internal conflict of the KMT; launched by Feng Yuxiang, Yan Xishan, and Wang Jingwei. The attention was turned to root out remaining pockets of CCP activity in a series of five encirclement campaigns. The first and second campaigns failed, and the third was aborted due to the Mukden Incident. The fourth campaign (1932–1933) achieved some early successes, but Chiang's armies were badly mauled when they tried to penetrate into the heart of Mao's Soviet Chinese Republic. During these campaigns, KMT columns struck swiftly into CCP areas, but were easily engulfed by the vast countryside and were not able to consolidate their foothold.

Finally, in late 1934, Chiang launched a fifth campaign that involved the systematic encirclement of the Jiangxi Soviet region with fortified blockhouses. The blockhouse strategy was devised and implemented in part by newly hired Nazi advisors. Unlike previous campaigns in which they penetrated deeply in a single strike, this time the KMT troops patiently built blockhouses, each separated by about 5 mi, to surround the Communist areas and cut off their supplies and food sources.

In October 1934, the CCP took advantage of gaps in the ring of blockhouses (manned by the forces of a warlord ally of Chiang Kai-shek's, rather than regular KMT troops) and broke out of the encirclement. The warlord armies were reluctant to challenge Communist forces for fear of losing their own men and did not pursue the CCP with much fervor. In addition, the main KMT forces were preoccupied with annihilating Zhang Guotao's army, which was much larger than Mao's. The massive military retreat of Communist forces lasted a year and covered what Mao estimated as 12,500 km (25,000 Li); it became known as the Long March.

This military retreat was undertaken by the Chinese Communist Party, led by Mao Zedong, to evade the pursuit or attack of the Kuomintang army. It consisted of a series of marches, during which numerous Communist armies in the south escaped to the north and west. Over the course of the march from Jiangxi the First Front Army, led by an inexperienced military commission, was on the brink of annihilation by Chiang Kai-Shek's troops as their stronghold was in Jiangxi. The Communists, under the command of Mao Zedong and Zhou Enlai, "escaped in a circling retreat to the west and north, which reportedly traversed over 9,000 kilometers over 370 days." The route passed through some of the most difficult terrain of western China by traveling west, and then northwards towards Shaanxi. "In November 1935, shortly after settling in northern Shaanxi, Mao officially took over Zhou Enlai's leading position in the Red Army. Following a major reshuffling of official roles, Mao became the chairman of the Military Commission, with Zhou and Deng Xiaoping as vice-chairmen." This marked Mao's position as the pre-eminent leader of the CCP, with Zhou in second position to him.

The march ended when the CCP reached the interior of Shaanxi. Zhang Guotao's army (Red 4th Front Army), which took a different route through northwest China, was largely destroyed by the forces of Chiang Kai-shek and his Chinese Muslim allies, the Ma clique. Along the way, the Communist army confiscated property and weapons from local warlords and landlords, while recruiting peasants and the poor, solidifying its appeal to the masses. Of the 90,000–100,000 people who began the Long March from the Soviet Chinese Republic, only around 7,000–8,000 made it to Shaanxi. The remnants of Zhang's forces eventually joined Mao in Shaanxi, but with his army destroyed, Zhang, even as a founding member of the CCP, was never able to challenge Mao's authority. Essentially, the great retreat made Mao the undisputed leader of the Chinese Communist Party.

The Kuomintang used Khampa troops—who were former bandits—to battle the Communist Red Army as it advanced and to undermine local warlords who often refused to fight Communist forces to conserve their own strength. The KMT enlisted 300 "Khampa bandits" into its Consolatory Commission military in Sichuan, where they were part of the effort of the central government to penetrate and destabilize local Han warlords such as Liu Wenhui. The government was seeking to exert full control over frontier areas against the warlords. Liu had refused to battle the Communists in order to conserve his army. The Consolatory Commission forces were used to battle the Red Army, but they were defeated when their religious leader was captured by the Communists.

In 1936, Zhou Enlai and Zhang Xueliang grew closer, with Zhou even suggesting that he join the CCP. However, this was turned down by the Comintern in the USSR. Later on, Zhou persuaded Zhang and Yang Hucheng, another warlord, to instigate the Xi'an Incident. Chiang was placed under house arrest and forced to stop his attacks on the Red Army, instead focusing on the Japanese threat.

Second Sino-Japanese War (1937–1945)
During Japan's invasion and occupation of Manchuria, Chiang Kai-shek saw the CCP as the greater threat. Chiang refused to ally with the CCP, preferring to unite China by eliminating the warlord and CCP forces first. He believed his forces were too weak to face the Japanese Imperial Army; only after unification could the KMT mobilize against Japan. He ignored the Chinese people's discontent and anger at the KMT policy of compromise with the Japanese, instead ordering KMT generals Zhang Xueliang and Yang Hucheng to suppress the CCP. However, their provincial forces suffered significant casualties in battles against the Red Army.

On 12 December 1936, the disgruntled Zhang and Yang conspired to kidnap Chiang and force him into a truce with the CCP. The incident became known as the Xi'an Incident. Both parties suspended fighting to form a Second United Front to focus their energies and fight the Japanese. In 1937, Japan launched its full-scale invasion of China and its well-equipped troops overran KMT defenders in northern and coastal China.

The alliance of CCP and KMT was in name only. Unlike the KMT forces, CCP troops shunned conventional warfare and instead waged guerrilla warfare against the Japanese. The level of actual cooperation and coordination between the CCP and KMT during World War II was minimal. In the midst of the Second United Front, the CCP and the KMT were still vying for territorial advantage in "Free China" (i.e., areas not occupied by the Japanese or ruled by Japanese puppet governments such as Manchukuo and the Reorganized National Government of China).

The situation came to a head in late 1940 and early 1941 when clashes between Communist and KMT forces intensified. Chiang demanded in December 1940 that the CCP's New Fourth Army evacuate Anhui and Jiangsu Provinces, due to its provocation and harassment of KMT forces in this area. Under intense pressure, the New Fourth Army commanders complied. The following year they were ambushed by KMT forces during their evacuation, which led to several thousand deaths. It also ended the Second United Front, formed earlier to fight the Japanese.

As clashes between the CCP and KMT intensified, countries such as the United States and the Soviet Union attempted to prevent a disastrous civil war. After the New Fourth Army incident, US President Franklin D. Roosevelt sent special envoy Lauchlin Currie to talk with Chiang Kai-shek and KMT party leaders to express their concern regarding the hostility between the two parties, with Currie stating that the only ones to benefit from a civil war would be the Japanese. The Soviet Union, allied more closely with the CCP, sent an imperative telegram to Mao in 1941, warning that civil war would also make the situation easier for the Japanese military. Due to the international community's efforts, there was a temporary and superficial peace. Chiang criticized the CCP in 1943 with the propaganda piece China's Destiny, which questioned the CCP's power after the war, while the CCP strongly opposed Chiang's leadership and referred to his regime as fascist in an attempt to generate a negative public image. Both leaders knew that a deadly battle had begun between themselves.

In general, developments in the Second Sino-Japanese War were to the advantage of the CCP, as its guerrilla war tactics had won them popular support within the Japanese-occupied areas. However, the KMT had to defend the country against the main Japanese campaigns, since it was the legal Chinese government, a factor which proved costly to Chiang Kai-shek and his troops. Japan launched its last major offensive against the KMT, Operation Ichi-Go, in 1944, which resulted in the severe weakening of Chiang's forces. The CCP also suffered fewer losses through its guerrilla tactics. By the end of the war, the Red Army had grown to more than 1.3 million members, with a separate militia of over 2.6 million. About one hundred million people lived in CCP-controlled zones.

Immediate post-war clashes (1945–1946)

Under the terms of the Japanese unconditional surrender dictated by the Allies, Japanese troops were to surrender to KMT troops but not to the CCP, which was present in some of the occupied areas. In Manchuria, however, where the KMT had no forces, the Japanese surrendered to the Soviet Union. Chiang Kai-shek reminded Japanese troops to remain at their posts to receive the KMT, but Communist forces soon began taking surrenders from the Japanese and fighting those who resisted. General Wedemeyer of the United States Army became alarmed at these developments and wanted seven American divisions to be sent to China, but General Marshall replied that it should not be given priority over Japan and Korea.

The first post-war peace negotiation, attended by both Chiang Kai-shek and Mao Zedong, was in Chongqing from 28 August to 10 October 1945. Chiang entered the meeting at an advantage because he had recently signed a friendly treaty with the Soviet Union while the Communists were still forcing the Japanese to surrender in some places. Mao was accompanied by American ambassador Patrick J. Hurley, who was devoted to Chiang but also wanted to ensure Mao's safety in light of the past history between the two Chinese leaders. It concluded with the signing of the Double Tenth Agreement. Both sides stressed the importance of a peaceful reconstruction, but the conference did not produce any concrete results. Battles between the two sides continued even as peace negotiations were in progress, until the agreement was reached in January 1946. However, large campaigns and full-scale confrontations between the CCP and Chiang's troops were temporarily avoided.

In the last month of World War II in East Asia, Soviet forces launched the huge Manchurian Strategic Offensive Operation against the Japanese Kwantung Army in Manchuria and along the Chinese-Mongolian border. This operation destroyed the Kwantung Army in just three weeks and left the USSR occupying all of Manchuria by the end of the war in a total power vacuum of local Chinese forces. Consequently, the 700,000 Japanese troops stationed in the region surrendered. Later in the year Chiang Kai-shek realized that he lacked the resources to prevent a CCP takeover of Manchuria following the scheduled Soviet departure. He therefore made a deal with the Soviets to delay their withdrawal until he had moved enough of his best-trained men and modern materiel into the region. However, the Soviets refused permission for the Nationalist troops to traverse its territory and spent the extra time systematically dismantling the extensive Manchurian industrial base (worth up to $2 billion) and shipping it back to their war-ravaged country. KMT troops were then airlifted by the US to occupy key cities in North China, while the countryside was already dominated by the CCP. On 15 November 1945, the KMT began a campaign to prevent the CCP from strengthening its already strong base. At the same time, however, the return of the KMT also brought widespread graft and corruption, with an OSS officer remarking that the only winners were the Communists.

In the winter of 1945–46, Joseph Stalin commanded Marshal Rodion Malinovsky to give Mao Zedong most Imperial Japanese Army weapons that were captured.

Chiang Kai-shek's forces pushed as far as Chinchow (Jinzhou) by 26 November 1945, meeting with little resistance. This was followed by a Communist offensive on the Shandong Peninsula that was largely successful, as all of the peninsula, except what was controlled by the US, fell to the Communists. The truce fell apart in June 1946 when full-scale war between CCP and KMT forces broke out on 26 June 1946. China then entered a state of civil war that lasted more than three years.

Background and disposition of forces
By the end of the Second Sino-Japanese War, the power of the Chinese Communist Party grew considerably. Their main force grew to 1.2 million troops, backed with additional militia of 2 million, totalling 3.2 million troops. Their "Liberated Zone" in 1945 contained 19 base areas, including one-quarter of the country's territory and one-third of its population; this included many important towns and cities. Moreover, the Soviet Union turned over all of its captured Japanese weapons and a substantial amount of their own supplies to the Communists, who received Northeastern China from the Soviets as well.

In March 1946, despite repeated requests from Chiang, the Soviet Red Army under the command of Marshal Rodion Malinovsky continued to delay pulling out of Manchuria, while Malinovsky secretly told the CCP forces to move in behind them, which led to full-scale war for the control of the Northeast. These favorable conditions also facilitated many changes inside the Communist leadership: the more radical hard-line faction who wanted a complete military take-over of China finally gained the upper hand and defeated the careful opportunists. Before giving control to Communist leaders, on 27 March, Soviet diplomats requested a joint venture of industrial development with the Nationalist Party in Manchuria.

Although General Marshall stated that he knew of no evidence that the CCP was being supplied by the Soviet Union, the CCP was able to utilize a large number of weapons abandoned by the Japanese, including some tanks. When large numbers of well-trained KMT troops began to defect to the Communist forces, the CCP was finally able to achieve material superiority. The CCP's most effective political reform was its land reform policy. This drew the massive number of landless and starving peasants in the countryside into the Communist cause. This strategy enabled the CCP to access an almost unlimited supply of manpower for both combat and logistical purposes; despite suffering heavy casualties throughout many of the war's campaigns, manpower continued to grow. For example, during the Huaihai Campaign alone the CCP was able to mobilize 5,430,000 peasants to fight against the KMT forces.

After the war with the Japanese ended, Chiang Kai-shek quickly moved KMT troops to newly liberated areas to prevent Communist forces from receiving the Japanese surrender. The US airlifted many KMT troops from central China to the Northeast (Manchuria). President Harry S. Truman was very clear about what he described as "using the Japanese to hold off the Communists". In his memoirs he writes:

"It was perfectly clear to us that if we told the Japanese to lay down their arms immediately and march to the seaboard, the entire country would be taken over by the Communists. We therefore had to take the unusual step of using the enemy as a garrison until we could airlift Chinese National troops to South China and send Marines to guard the seaports."

Using the pretext of "receiving the Japanese surrender", business interests within the KMT government occupied most of the banks, factories and commercial properties, which had previously been seized by the Imperial Japanese Army. They also conscripted troops at an accelerated pace from the civilian population and hoarded supplies, preparing for a resumption of war with the Communists. These hasty and harsh preparations caused great hardship for the residents of cities such as Shanghai, where the unemployment rate rose dramatically to 37.5%.

Hyperinflation meant those employed in the Kuomintang forces lost the purchasing power of their pay. This resulted in corruption and the embezzlement of supplies which disappeared into the barter economy. Ordinary Kuomintang soldiers were often malnourished and desertion was common.

The US strongly supported the Kuomintang forces. About 50,000 US soldiers were sent to guard strategic sites in Hebei and Shandong in Operation Beleaguer. The US equipped and trained KMT troops, and transported Japanese and Koreans back to help KMT forces to occupy liberated zones as well as to contain Communist-controlled areas. According to William Blum, American aid included substantial amounts of mostly surplus military supplies, and loans were made to the KMT. Within less than two years after the Sino-Japanese War, the KMT had received $4.43 billion from the US—most of which was military aid. Highlighting the aid provided by the US to the KMT, the Communists' position was that the US was stirring domestic warfare and characterized the civil war as both a national revolution against the KMT and a revolution against US colonization and aggression.

Outbreak of war
As postwar negotiations between the Nationalist government and the CCP failed, the civil war between these two parties resumed. This stage of war is referred to in mainland China and Communist historiography as the "War of Liberation". On 20 July 1946, Chiang Kai-shek launched a large-scale assault on Communist territory in North China with 113 brigades (a total of 1.6 million troops).

Knowing their disadvantages in manpower and equipment, the CCP executed a "passive defense" strategy. It avoided the strong points of the KMT army and was prepared to abandon territory in order to preserve its forces. In most cases the surrounding countryside and small towns had come under Communist influence long before the cities. The CCP also attempted to wear out the KMT forces as much as possible. This tactic seemed to be successful; after a year, the power balance became more favorable to the CCP. They wiped out 1.12 million KMT troops, while their strength grew to about two million men.

In March 1947, the KMT achieved a symbolic victory by seizing Yan'an, the capital of the Yan'an Soviet. The Communists counterattacked soon afterwards; on 30 June 1947, CCP troops crossed the Yellow River and moved to the Dabie Mountains area, restored and developed the Central Plain. At the same time, Communist forces also began to counterattack in Northeastern China, North China and East China.

By late 1948, the CCP captured the northern cities of Shenyang and Changchun and seized control of the Northeast after suffering numerous setbacks while trying to take the cities, with the decisive Liaoshen Campaign. The New 1st Army, regarded as the best KMT army, was forced to surrender after the CCP conducted a brutal six-month siege of Changchun that resulted in more than 150,000 civilian deaths from starvation.

The capture of large KMT units provided the CCP with the tanks, heavy artillery and other combined-arms assets needed to execute offensive operations south of the Great Wall. By April 1948, the city of Luoyang fell, cutting the KMT army off from Xi'an. Following a fierce battle, the CCP captured Jinan and Shandong province on 24 September 1948. The Huaihai Campaign of late 1948 and early 1949 secured east-central China for the CCP. A large number of KMT troops deserted and changed sides in these conflicts. The outcome of these encounters were decisive for the military outcome of the civil war.

The Pingjin Campaign resulted in the Communist conquest of northern China. It lasted 64 days, from 21 November 1948 to 31 January 1949. The PLA suffered heavy casualties while securing Zhangjiakou, Tianjin along with its port and garrison at Dagu and Beiping. The CCP brought 890,000 troops from the northeast to oppose some 600,000 KMT troops. There were 40,000 CCP casualties at Zhangjiakou alone. They in turn killed, wounded or captured some 520,000 KMT during the campaign.

After achieving decisive victory at Liaoshen, Huaihai and Pingjin campaigns, the CCP destroyed 144 regular and 29 irregular KMT divisions, including 1.54 million veteran KMT troops, which significantly reduced the strength of Nationalist forces. Stalin initially favored a coalition government in postwar China, and tried to persuade Mao to stop the CCP from crossing the Yangtze and attacking the KMT positions south of the river. Mao rejected Stalin's position and on 21 April, began the Yangtze River Crossing Campaign. On 23 April, they captured the KMT's capital, Nanjing. The KMT government retreated to Canton (Guangzhou) until 15 October, Chongqing until 25 November, and then Chengdu before retreating to Taiwan on 7 December. By late 1949, the People's Liberation Army was pursuing remnants of KMT forces southwards in southern China, and only Tibet was left. A Chinese Muslim Hui cavalry regiment, the 14th Tungan Cavalry, was sent by the Kuomintang to attack Mongol and Soviet positions along the border during the Pei-ta-shan Incident.

The Kuomintang made several last-ditch attempts to use Khampa troops against the Communists in southwest China. The Kuomintang formulated a plan in which three Khampa divisions would be assisted by the Panchen Lama to oppose the Communists. Kuomintang intelligence reported that some Tibetan tusi chiefs and the Khampa Su Yonghe controlled 80,000 troops in Sichuan, Qinghai and Tibet. They hoped to use them against the Communist army.

Pushing south
On 1 October 1949, Mao Zedong proclaimed the founding of the People's Republic of China with its capital at Beiping, which was returned to the former name Beijing. Chiang Kai-shek and approximately two million Nationalist soldiers retreated from mainland China to the island of Taiwan in December after the PLA advanced into Sichuan province. Isolated Nationalist pockets of resistance remained in the area, but the majority of the resistance collapsed after the fall of Chengdu on 10 December 1949, with some resistance continuing in the far south.

A PRC attempt to take the ROC-controlled island of Quemoy was thwarted in the Battle of Kuningtou, halting the PLA advance towards Taiwan. In December 1949, Chiang proclaimed Taipei the temporary capital of the Republic of China and continued to assert his government as the sole legitimate authority in China.

The Communists' other amphibious operations of 1950 were more successful: they led to the Communist conquest of Hainan Island in April 1950, the Wanshan Islands off the Guangdong coast (May–August 1950), and Zhoushan Island off Zhejiang (May 1950).

Aftermath and unsolved issues (1949–present)

Most observers expected Chiang's government to eventually fall to the imminent invasion of Taiwan by the People's Liberation Army, and the US was initially reluctant in offering full support for Chiang in their final stand. US President Harry S. Truman announced on 5 January 1950 that the United States would not engage in any dispute involving the Taiwan Strait, and that he would not intervene in the event of an attack by the PRC. Truman, seeking to exploit the possibility of a Titoist-style Sino-Soviet split, announced in his United States Policy toward Formosa that the US would obey the Cairo Declaration's designation of Taiwan as Chinese territory and would not assist the Nationalists. However, the Communist leadership was not aware of this change of policy, instead becoming increasingly hostile to the US. The situation quickly changed after the sudden onset of the Korean War in June 1950. This led to changing political climate in the US, and President Truman ordered the United States Seventh Fleet to sail to the Taiwan Strait as part of the containment policy against potential Communist advance.

In June 1949, the ROC declared a "closure" of all mainland China ports and its navy attempted to intercept all foreign ships. The closure was from a point north of the mouth of Min River in Fujian to the mouth of the Liao River in Liaoning. Since mainland China's railroad network was underdeveloped, north–south trade depended heavily on sea lanes. ROC naval activity also caused severe hardship for mainland China fishermen.

During the retreat of the Republic of China to Taiwan, KMT troops, who could not retreat to Taiwan, were left behind to fight a guerrilla war against the Communists. These KMT remnants were eliminated in what the PRC called the Campaign to Suppress Counterrevolutionaries and the Campaigns to Suppress Bandits. According to official statistics from the CCP in 1954, during the Campaign to Suppress Counterrevolutionaries, at least 2.6 million people were arrested, some 1.29 million people were imprisoned, and 712,000 people were executed. Most of those killed were former Kuomintang officials, businessmen, former employees of Western companies and intellectuals whose loyalty was suspect.

Winning China proper in 1950, also after annexation of Tibet, the CCP controlled the entire mainland in late 1951 (excluding Kinmen and Matsu Islands). But a group of approximately 3,000 KMT Central soldiers retreated to Burma and continued launching guerrilla attacks into south China during the Kuomintang Islamic Insurgency in China (1950–1958) and Campaign at the China–Burma Border. Their leader, Li Mi, was paid a salary by the ROC government and given the nominal title of Governor of Yunnan. Initially, the US-supported these remnants and the Central Intelligence Agency provided them with military aid. After the Burmese government appealed to the United Nations in 1953, the US began pressuring the ROC to withdraw its loyalists. By the end of 1954 nearly 6,000 soldiers had left Burma and Li declared his army disbanded. However, thousands remained, and the ROC continued to supply and command them, even secretly supplying reinforcements at times to maintain a base close to China.

After the ROC complained to the United Nations against the Soviet Union for violating the Sino-Soviet Treaty of Friendship and Alliance to support the CCP, the UN General Assembly Resolution 505 was adopted on 1 February 1952, condemning the Soviet Union.

In the end, the Communist military forces suffered 1.3 million combat casualties in the 1945–1949 phase of the war: 260,000 killed, 190,000 missing, and 850,000 wounded, discounting irregulars. Nationalist casualties in the same phase were recorded after the war by the PRC 5,452,700 regulars and 2,258,800 irregulars.

After the formation of the PRC, the PRC government named the Western nations, led by the U.S., as the biggest threat to its national security. Basing this judgment on multiple factors, including the idea of a Chinese century of humiliation at the hands of Western powers beginning in the mid-19th century, U.S. support for the Nationalists during the Chinese Civil War, and the ideological struggles between revolutionaries and reactionaries, the PRC Chinese leadership believed that China would become a critical battleground in the U.S.' crusade against Communism. As a countermeasure and to elevate China's standing among the worldwide Communist movements, the PRC leadership adopted a foreign policy that actively promoted Communist revolutions throughout territories on China's periphery.

Taiwan Strait tensions
Though viewed as a military liability by the US, the ROC viewed its remaining islands in Fujian as vital for any future campaign to defeat the PRC and retake mainland China. On 3 September 1954, the First Taiwan Strait Crisis started with the PRC shelling Kinmen. The PRC captured the Yijiangshan Islands on 19 January 1955, leading to the ROC abandoning the Dachen Islands the following month. On 24 January 1955, the United States Congress passed the Formosa Resolution authorizing the President to defend the ROC's offshore islands. The First Taiwan Straits crisis ended in March 1955 when the PLA ceased its bombardment. The crisis ended during the Bandung conference.

The Second Taiwan Strait Crisis began on 23 August 1958 with air and naval engagements between PRC and ROC forces, leading to intense artillery bombardment of Kinmen by the PRC and Xiamen by the ROC, and ended on November of the same year. PLA patrol boats blockaded the islands from ROC supply ships. Though the US rejected Chiang Kai-shek's proposal to bomb mainland China artillery batteries, it quickly moved to supply fighter jets and anti-aircraft missiles to the ROC. It also provided amphibious assault ships to land supplies, as a sunken ROC naval vessel was blocking the harbor. On 7 September, the US escorted a convoy of ROC supply ships and the PRC refrained from firing.

The third crisis occurred in 1995–96. The PRC responded to Taiwanese President Lee Teng-hui's visit to the United States, and the U.S. recognition of Lee as a representative of Taiwan, with military exercises. The exercises were also meant to deter Taiwanese voters from supporting Lee in the 1996 election; Lee won the election. Two U.S. aircraft carriers were deployed during the crisis; they were not attacked and deescalation followed.

US Speaker of the House Nancy Pelosi's visit to Taiwan in August 2022 triggered PRC military exercises across the Taiwan Strait. She originally intended to travel to Taiwan in April 2022, but was delayed due to COVID-19. She rescheduled the trip to August as part of a wider Asian trip. The White House was reported to have been initially divided over the appropriateness of the trip but later affirmed Pelosi's right to visit Taiwan. As a result, the PLA announced four days of unprecedented military live-fire drills, in six zones that encircle the island on the busiest international waterways and aviation routes. In response to the announcement, ROC officials complained that the PRC's live-fire drills were an invasion of Taiwan's territorial space and a direct challenge to free air and sea navigation.

Political fallout
On 25 October 1971, the United Nations General Assembly admitted the PRC and expelled the ROC, which had been a founding member of the United Nations and was one of the five permanent members of the Security Council. Representatives of Chiang Kai-shek refused to recognise their accreditations as representatives of China and left the assembly. Recognition for the People's Republic of China soon followed from most other member nations, including the United States.

By 1984, PRC and ROC began to de-escalate their hostilities through diplomatic relations with each other, and cross-straits trade and investment has been growing ever since. The state of war was officially declared over by the ROC in 1991. Despite the end of the hostilities, the two sides have never signed any agreement or treaty to officially end the war. According to Mao Zedong, there were three ways of "staving off imperialist intervention in the short term" during the continuation of the Chinese Revolution. The first was through a rapid completion of the military takeover of the country, and through showing determination and strength against "foreign attempts at challenging the new regime along its borders". The second was by "formalising a comprehensive military alliance with the Soviet Union", which would dedicate Soviet power to directly defending China against its enemies; this aspect became extensively significant given the backdrop of the start of the Cold War. And finally, the regime had to "root out its domestic opponents: the heads of secret societies, religious sects, independent unions, or tribal and ethnic organisations". By destroying the basis of domestic reaction, Mao believed a safer world for the Chinese revolution to spread in would come into existence.

Under the new ROC president Lee Teng-hui, the Temporary Provisions Effective During the Period of Communist Rebellion was renounced in May 1991, thus ending the chances of the Kuomintang's quest to retake the mainland. In July 1999, Lee announced a "special diplomatic relationship". China was furious again, but the military drills were stopped by the 921 earthquakes. It was the last tense moment of this civil war.

With the election in 2000 of Democratic Progressive Party candidate Chen Shui-bian, a party other than the KMT gained the presidency for the first time in Taiwan. The new president did not share the Chinese nationalist ideology of the KMT and CCP. This led to tension between the two sides, although trade and other ties such as the 2005 Pan-Blue visit continued to increase.

With the election of pro-mainland President Ma Ying-jeou (KMT) in 2008, significant warming of relations resumed between Taipei and Beijing, with high-level exchanges between the semi-official diplomatic organizations of both states such as the Chen-Chiang summit series. Although the Taiwan Strait remains a potential flash point, regular direct air links were established in 2009.

Reasons for the Communist victory
The CCP victory over the Nationalists is regarded as one of the most impressive twentieth century insurgent victories. Historians and political scientists cite a number of factors, including the CCP's success at mobilizing mass support and the shortcomings of the Nationalist government.

Poor governance by Nationalists
Almost all studies of the failure of the Nationalist government identify hyperinflation as a major factor in the government's collapse. The Nationalist military and the government's civilian employees were most impacted by hyperinflation which in turn prompted widespread corruption and pilfering. Little funding reached enlisted soldiers, who were typically malnourished and poorly equipped. Desertion was common.

The historian Rana Mitter writes that a lack of trust in the Nationalist government developed, as it was increasingly seen as "corrupt, vindictive, and with no overall vision of what China under its rule should look like". Chiang wrote in his diary in June 1948: "After the fall of Kaifeng our conditions worsened and became more serious. I now realized that the main reason our nation has collapsed, time after time throughout our history, was not because of superior power used by our external enemies, but because of disintegration and rot from within."

Historian Odd Arne Westad says the Communists won the Civil War because they made fewer military mistakes than Chiang Kai-shek and also because in his search for a powerful centralized government, Chiang antagonized too many interest groups in China. Furthermore, his party was weakened in the war against the Japanese. Meanwhile, the Communists targeted different groups, such as peasants, and brought them to their side. After 1945, the economy in the ROC areas collapsed because of hyperinflation and the failure of price controls by the ROC government and financial reforms; the Gold Yuan devaluated sharply in late 1948 and resulted in the ROC government losing the support of the cities' middle classes.

United States Secretary of State Dean Acheson described the Nationalists as "corrupt, reactionary, and inefficient." He believed that the Nationalists had displayed both political inadequacy as well as "the grossest incompetence ever experienced by any military command," and that the Communists "did not create this condition," but skillfully exploited the opportunity it provided.

Popular support for Communists and cohesion
In the meantime, the Communists continued their land reform programs, winning the support of the population in the countryside. This was a decisive factor in the Communists' success. Millions of peasants who obtained land through the movement joined the People's Liberation Army or assisted in its logistical networks. According to historian Brian DeMare, land redistribution was a critical factor because it linked the interests of peasants in the north and northeast to the Communists' success. Ultimately, the Communists obtained the greatest popular support of any insurgency in modern history.

An important advantage of the Communists was the "extraordinary cohesion" within its top leadership. This cohesion not only secured it from defections during difficult times but also facilitated "communications and top level debates over tactics". The charismatic style of leadership of Mao Zedong created a "unity of purpose" and a "unity of command" which the KMT lacked. Apart from that, the CCP had mastered the manipulation of local politics to their benefit; this was also derived from their propaganda skills that had also been decentralised successfully by portraying their opponents as "enemies of all groups of Chinese" and itself as "defenders of the nation" and people (given the backdrop of the war with Japan).

International factors
Strong American support for the Nationalists was hedged with the failure of the Marshall Mission, and then stopped completely mainly because of KMT corruption (such as the notorious Yangtze Development Corporation controlled by H.H. Kung and T. V. Soong's family) and KMT's military setback in Northeast China. Historians such as Jay Taylor, Robert Cowley, and Anne W. Carroll argue that the Nationalists' failure was largely caused by external reasons outside of the KMT's control, most notably the refusal of the Truman administration to support Chiang with the withdrawal of aid, the US armed embargo, the failed pursuit of a détente between the Nationalists and the communists, and the USSR's consistent support of the CCP in the Chinese Civil War. The better-trained Communist army's support from the USSR helped counter the American aid that the Nationalists received. Chen Yun said: "They did their best to help us, we were backed by the Soviet Union and North Korea."

Atrocities
During the war, both the Nationalists and Communists carried out mass atrocities, with millions of non-combatants deliberately killed by both sides. Benjamin Valentino has estimated atrocities in the Chinese Civil War resulted in the death of between 1.8 million and 3.5 million people between 1927 and 1949.

Nationalist atrocities
Over several years after the 1927 Shanghai massacre, the Kuomintang killed between 300,000 and one million people, primarily peasants, in anti-communist campaigns as part of the White Terror. During the White Terror, the Nationalists specifically targeted women with short hair who had not been subjected to foot binding, on the presumption that such "non-traditional" women were radicals. Nationalist forces cut off their breasts, shaved their heads, and displayed their mutilated bodies to intimidate the populace.

Torture, rape, and collective punishment were common Nationalist practices during its counter-insurgency campaigns. The Nationalists uprooted and moved entire communities in an effort to more easily monitor Communist activities.

From 1946 to 1949, the Nationalists arrested, tortured, and killed political dissidents via the Sino-American Cooperative Organization.

Communist atrocities
During the December 1930 Futian incident, the communists executed 2,000 to 3,000 members of the Futian battalion after its leaders had mutinied against Mao Zedong.

Between 1931 and 1934 in the Jiangxi–Fujian Soviet, the communist authorities engaged in a widespread campaign of violence against civilians to ensure compliance with its policies and to stop defection to the advancing KMT, including mass executions, land confiscation and forced labor. According to Li Weihan, a high-ranking communist in Jiangxi at the time, in response to mass flight of civilians to KMT held areas, the local authorities would "usually to send armed squads after those attempting to flee and kill them on the spot, producing numerous mass graves throughout the CSR [Chinese Soviet Republic in Jiangxi] that would later be uncovered by the KMT and its allies." Zhang Wentian, another high-ranking communist, reported that "the policy of annihilating landlords as an exploiting class had degenerated into a massacre" The population of the communist controlled area fell by 700,000 from 1931 and 1935, of which a large proportion were murdered as "class enemies", worked to death, committed suicide, or died in other circumstances attributable to the communists.

During the Siege of Changchun, the People's Liberation Army implemented a military blockade on the KMT-held city of Changchun and prevented civilians from leaving the city during the blockade; this blockade caused the starvation of tens to 150 thousand civilians. The PLA continued to use siege tactics throughout Northeast China.

At the outbreak of the Chinese Civil War in 1946, Mao Zedong began to push for a return to radical policies to mobilize China against the landlord class, but protected the rights of middle peasants and specified that rich peasants were not landlords. The 7 July Directive of 1946 set off eighteen months of fierce conflict in which all rich peasant and landlord property of all types was to be confiscated and redistributed to poor peasants. CCP work teams went quickly from village to village and divided the population into landlords, rich, middle, poor, and landless peasants. Because the work teams did not involve villagers in the process, however, rich and middle peasants quickly returned to power. The Outline Land Law of October 1947 increased the pressure. Those condemned as landlords were buried alive, dismembered, strangled and shot. In response to the aforementioned land reform campaign, the Kuomintang helped establish the "Huanxiang Tuan", or Homecoming Legion, which was composed of landlords who sought the return of their redistributed land and property from peasants and CCP guerrillas, as well as forcibly conscripted peasants and communist POWs. The Homecoming legion conducted its guerrilla warfare campaign against CCP forces and purported collaborators up until the end of the civil war in 1949.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

title: Chinese Civil War


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Phase transition

In physics, chemistry, and other related fields like biology, a phase transition (or phase change) is the physical process of transition between one state of a medium and another. Commonly the term is used to refer to changes among the basic states of matter: solid, liquid, and gas, and in rare cases, plasma. A phase of a thermodynamic system and the states of matter have uniform physical properties. During a phase transition of a given medium, certain properties of the medium change as a result of the change of external conditions, such as temperature or pressure. This can be a discontinuous change; for example, a liquid may become gas upon heating to its boiling point, resulting in an abrupt change in volume. The identification of the external conditions at which a transformation occurs defines the phase transition point.

States of matter

Phase transitions commonly refer to when a substance transforms between one of the four states of matter to another. At the phase transition point for a substance, for instance the boiling point, the two phases involved - liquid and vapor, have identical free energies and therefore are equally likely to exist. Below the boiling point, the liquid is the more stable state of the two, whereas above the boiling point the gaseous form is the more stable.

Common transitions between the solid, liquid, and gaseous phases of a single component, due to the effects of temperature and/or pressure are identified in the following table:

For a single component, the most stable phase at different temperatures and pressures can be shown on a phase diagram. Such a diagram usually depicts states in equilibrium. A phase transition usually occurs when the pressure or temperature changes and the system crosses from one region to another, like water turning from liquid to solid as soon as the temperature drops below the freezing point. In exception to the usual case, it is sometimes possible to change the state of a system diabatically (as opposed to adiabatically) in such a way that it can be brought past a phase transition point without undergoing a phase transition. The resulting state is metastable, i.e., less stable than the phase to which the transition would have occurred, but not unstable either. This occurs in superheating and supercooling, for example. Metastable states do not appear on usual phase diagrams.

Structural

Phase transitions can also occur when a solid changes to a different structure without changing its chemical makeup. In elements, this is known as allotropy, whereas in compounds it is known as polymorphism. The change from one crystal structure to another, from a crystalline solid to an amorphous solid, or from one amorphous structure to another (polyamorphs) are all examples of solid to solid phase transitions.

The martensitic transformation occurs as one of the many phase transformations in carbon steel and stands as a model for displacive phase transformations. Order-disorder transitions such as in alpha-titanium aluminides. As with states of matter, there are also a metastable to equilibrium phase transformation for structural phase transitions. A metastable polymorph which forms rapidly due to lower surface energy will transform to an equilibrium phase given sufficient thermal input to overcome an energetic barrier.

Magnetic

Phase transitions can also describe the change between different kinds of magnetic ordering. The most well-known is the transition between the ferromagnetic and paramagnetic phases of magnetic materials, which occurs at what is called the Curie point. Another example is the transition between differently ordered, commensurate or incommensurate, magnetic structures, such as in cerium antimonide. A simplified but highly useful model of magnetic phase transitions is provided by the Ising Model

Mixtures

Phase transitions involving solutions and mixtures are more complicated than transitions involving a single compound. While chemically pure compounds exhibit a single temperature melting point between solid and liquid phases, mixtures can either have a single melting point, known as congruent melting, or they have different liquidus and solidus temperatures resulting in a temperature span where solid and liquid coexist in equilibrium. This is often the case in solid solutions, where the two components are isostructural.

There are also a number of phase transitions involving three phases: a eutectic transformation, in which a two-component single-phase liquid is cooled and transforms into two solid phases. The same process, but beginning with a solid instead of a liquid is called a eutectoid transformation. A peritectic transformation, in which a two-component single-phase solid is heated and transforms into a solid phase and a liquid phase. A peritectoid reaction is a peritectoid rection, except involving only solid phases. A monotectic reaction consists of change from a liquid and to a combination of a solid and a second liquid, where the two liquids display a miscibility gap.

Separation into multiple phases can occur via spinodal decomposition, in which a single phase is cooled and separates into two different compositions.

Non-equilibrium mixtures can occur, such as in supersaturation.

Other examples
Other phase changes include:

 * Transition to a mesophase between solid and liquid, such as one of the "liquid crystal" phases.
 * The dependence of the adsorption geometry on coverage and temperature, such as for hydrogen on iron (110).
 * The emergence of superconductivity in certain metals and ceramics when cooled below a critical temperature.
 * The emergence of metamaterial properties in artificial photonic media as their parameters are varied.
 * Quantum condensation of bosonic fluids (Bose–Einstein condensation). The superfluid transition in liquid helium is an example of this.
 * The breaking of symmetries in the laws of physics during the early history of the universe as its temperature cooled.
 * Isotope fractionation occurs during a phase transition, the ratio of light to heavy isotopes in the involved molecules changes. When water vapor condenses (an equilibrium fractionation), the heavier water isotopes (18O and 2H) become enriched in the liquid phase while the lighter isotopes (16O and 1H) tend toward the vapor phase.

Phase transitions occur when the thermodynamic free energy of a system is non-analytic for some choice of thermodynamic variables (cf. phases). This condition generally stems from the interactions of a large number of particles in a system, and does not appear in systems that are small. Phase transitions can occur for non-thermodynamic systems, where temperature is not a parameter. Examples include: quantum phase transitions, dynamic phase transitions, and topological (structural) phase transitions. In these types of systems other parameters take the place of temperature. For instance, connection probability replaces temperature for percolating networks.

Ehrenfest classification
Paul Ehrenfest classified phase transitions based on the behavior of the thermodynamic free energy as a function of other thermodynamic variables. Under this scheme, phase transitions were labeled by the lowest derivative of the free energy that is discontinuous at the transition. First-order phase transitions exhibit a discontinuity in the first derivative of the free energy with respect to some thermodynamic variable. The various solid/liquid/gas transitions are classified as first-order transitions because they involve a discontinuous change in density, which is the (inverse of the) first derivative of the free energy with respect to pressure. Second-order phase transitions are continuous in the first derivative (the order parameter, which is the first derivative of the free energy with respect to the external field, is continuous across the transition) but exhibit discontinuity in a second derivative of the free energy. These include the ferromagnetic phase transition in materials such as iron, where the magnetization, which is the first derivative of the free energy with respect to the applied magnetic field strength, increases continuously from zero as the temperature is lowered below the Curie temperature. The magnetic susceptibility, the second derivative of the free energy with the field, changes discontinuously. Under the Ehrenfest classification scheme, there could in principle be third, fourth, and higher-order phase transitions. For example, the Gross–Witten–Wadia phase transition in 2-d lattice quantum chromodynamics is a third-order phase transition. The Curie points of many ferromagnetics is also a third-order transition, as shown by their specific heat having a sudden change in slope.

In practice, only the first- and second-order phase transitions are typically observed. The second-order phase transition was for a while controversial, as it seems to require two sheets of the Gibbs free energy to osculate exactly, which is so unlikely as to never occur in practice. Cornelis Gorter replied the criticism by pointing out that the Gibbs free energy surface might have two sheets on one side, but only one sheet on the other side, creating a forked appearance. ( pp. 146--150)

The Ehrenfest classification implicitly allows for continuous phase transformations, where the bonding character of a material changes, but there is no discontinuity in any free energy derivative. An example of this occurs at the supercritical liquid–gas boundaries.

The first example of a phase transition which did not fit into the Ehrenfest classification was the exact solution of the Ising model, discovered in 1944 by Lars Onsager. The exact specific heat differed from the earlier mean-field approximations, which had predicted that it has a simple discontinuity at critical temperature. Instead, the exact specific heat had a logarithmic divergence at the critical temperature. In the following decades, the Ehrenfest classification was replaced by a simplified classification scheme that is able to incorporate such transitions.

Modern classifications
In the modern classification scheme, phase transitions are divided into two broad categories, named similarly to the Ehrenfest classes:

First-order phase transitions are those that involve a latent heat. During such a transition, a system either absorbs or releases a fixed (and typically large) amount of energy per volume. During this process, the temperature of the system will stay constant as heat is added: the system is in a "mixed-phase regime" in which some parts of the system have completed the transition and others have not.

Familiar examples are the melting of ice or the boiling of water (the water does not instantly turn into vapor, but forms a turbulent mixture of liquid water and vapor bubbles). Yoseph Imry and Michael Wortis showed that quenched disorder can broaden a first-order transition. That is, the transformation is completed over a finite range of temperatures, but phenomena like supercooling and superheating survive and hysteresis is observed on thermal cycling.

s are also called "continuous phase transitions". They are characterized by a divergent susceptibility, an infinite correlation length, and a power law decay of correlations near criticality. Examples of second-order phase transitions are the ferromagnetic transition, superconducting transition (for a Type-I superconductor the phase transition is second-order at zero external field and for a Type-II superconductor the phase transition is second-order for both normal-state–mixed-state and mixed-state–superconducting-state transitions) and the superfluid transition. In contrast to viscosity, thermal expansion and heat capacity of amorphous materials show a relatively sudden change at the glass transition temperature which enables accurate detection using differential scanning calorimetry measurements. Lev Landau gave a phenomenological theory of second-order phase transitions.

Apart from isolated, simple phase transitions, there exist transition lines as well as multicritical points, when varying external parameters like the magnetic field or composition.

Several transitions are known as infinite-order phase transitions. They are continuous but break no symmetries. The most famous example is the Kosterlitz–Thouless transition in the two-dimensional XY model. Many quantum phase transitions, e.g., in two-dimensional electron gases, belong to this class.

The liquid–glass transition is observed in many polymers and other liquids that can be supercooled far below the melting point of the crystalline phase. This is atypical in several respects. It is not a transition between thermodynamic ground states: it is widely believed that the true ground state is always crystalline. Glass is a quenched disorder state, and its entropy, density, and so on, depend on the thermal history. Therefore, the glass transition is primarily a dynamic phenomenon: on cooling a liquid, internal degrees of freedom successively fall out of equilibrium. Some theoretical methods predict an underlying phase transition in the hypothetical limit of infinitely long relaxation times. No direct experimental evidence supports the existence of these transitions.

Phase coexistence
A disorder-broadened first-order transition occurs over a finite range of temperatures where the fraction of the low-temperature equilibrium phase grows from zero to one (100%) as the temperature is lowered. This continuous variation of the coexisting fractions with temperature raised interesting possibilities. On cooling, some liquids vitrify into a glass rather than transform to the equilibrium crystal phase. This happens if the cooling rate is faster than a critical cooling rate, and is attributed to the molecular motions becoming so slow that the molecules cannot rearrange into the crystal positions. This slowing down happens below a glass-formation temperature Tg, which may depend on the applied pressure. If the first-order freezing transition occurs over a range of temperatures, and Tg falls within this range, then there is an interesting possibility that the transition is arrested when it is partial and incomplete. Extending these ideas to first-order magnetic transitions being arrested at low temperatures, resulted in the observation of incomplete magnetic transitions, with two magnetic phases coexisting, down to the lowest temperature. First reported in the case of a ferromagnetic to anti-ferromagnetic transition, such persistent phase coexistence has now been reported across a variety of first-order magnetic transitions. These include colossal-magnetoresistance manganite materials, magnetocaloric materials, magnetic shape memory materials, and other materials. The interesting feature of these observations of Tg falling within the temperature range over which the transition occurs is that the first-order magnetic transition is influenced by magnetic field, just like the structural transition is influenced by pressure. The relative ease with which magnetic fields can be controlled, in contrast to pressure, raises the possibility that one can study the interplay between Tg and Tc in an exhaustive way. Phase coexistence across first-order magnetic transitions will then enable the resolution of outstanding issues in understanding glasses.

Critical points
In any system containing liquid and gaseous phases, there exists a special combination of pressure and temperature, known as the critical point, at which the transition between liquid and gas becomes a second-order transition. Near the critical point, the fluid is sufficiently hot and compressed that the distinction between the liquid and gaseous phases is almost non-existent. This is associated with the phenomenon of critical opalescence, a milky appearance of the liquid due to density fluctuations at all possible wavelengths (including those of visible light).

Symmetry
Phase transitions often involve a symmetry breaking process. For instance, the cooling of a fluid into a crystalline solid breaks continuous translation symmetry: each point in the fluid has the same properties, but each point in a crystal does not have the same properties (unless the points are chosen from the lattice points of the crystal lattice). Typically, the high-temperature phase contains more symmetries than the low-temperature phase due to spontaneous symmetry breaking, with the exception of certain accidental symmetries (e.g. the formation of heavy virtual particles, which only occurs at low temperatures).

Order parameters
An order parameter is a measure of the degree of order across the boundaries in a phase transition system; it normally ranges between zero in one phase (usually above the critical point) and nonzero in the other. At the critical point, the order parameter susceptibility will usually diverge.

An example of an order parameter is the net magnetization in a ferromagnetic system undergoing a phase transition. For liquid/gas transitions, the order parameter is the difference of the densities.

From a theoretical perspective, order parameters arise from symmetry breaking. When this happens, one needs to introduce one or more extra variables to describe the state of the system. For example, in the ferromagnetic phase, one must provide the net magnetization, whose direction was spontaneously chosen when the system cooled below the Curie point. However, note that order parameters can also be defined for non-symmetry-breaking transitions.

Some phase transitions, such as superconducting and ferromagnetic, can have order parameters for more than one degree of freedom. In such phases, the order parameter may take the form of a complex number, a vector, or even a tensor, the magnitude of which goes to zero at the phase transition.

There also exist dual descriptions of phase transitions in terms of disorder parameters. These indicate the presence of line-like excitations such as vortex- or defect lines.

Relevance in cosmology
Symmetry-breaking phase transitions play an important role in cosmology. As the universe expanded and cooled, the vacuum underwent a series of symmetry-breaking phase transitions. For example, the electroweak transition broke the SU(2)×U(1) symmetry of the electroweak field into the U(1) symmetry of the present-day electromagnetic field. This transition is important to explain the asymmetry between the amount of matter and antimatter in the present-day universe, according to electroweak baryogenesis theory.

Progressive phase transitions in an expanding universe are implicated in the development of order in the universe, as is illustrated by the work of Eric Chaisson and David Layzer.

See also relational order theories and order and disorder.

Critical exponents and universality classes
Continuous phase transitions are easier to study than first-order transitions due to the absence of latent heat, and they have been discovered to have many interesting properties. The phenomena associated with continuous phase transitions are called critical phenomena, due to their association with critical points.

Continuous phase transitions can be characterized by parameters known as critical exponents. The most important one is perhaps the exponent describing the divergence of the thermal correlation length by approaching the transition. For instance, let us examine the behavior of the heat capacity near such a transition. We vary the temperature T of the system while keeping all the other thermodynamic variables fixed and find that the transition occurs at some critical temperature Tc. When T is near Tc, the heat capacity C typically has a power law behavior:
 * $$C \propto |T_\text{c} - T|^{-\alpha}.$$

The heat capacity of amorphous materials has such a behaviour near the glass transition temperature where the universal critical exponent α = 0.59 A similar behavior, but with the exponent ν instead of α, applies for the correlation length.

The exponent ν is positive. This is different with α. Its actual value depends on the type of phase transition we are considering.

The critical exponents are not necessarily the same above and below the critical temperature. When a continuous symmetry is explicitly broken down to a discrete symmetry by irrelevant (in the renormalization group sense) anisotropies, then some exponents (such as $$\gamma$$, the exponent of the susceptibility) are not identical.

For −1 < α < 0, the heat capacity has a "kink" at the transition temperature. This is the behavior of liquid helium at the lambda transition from a normal state to the superfluid state, for which experiments have found α = −0.013 ± 0.003. At least one experiment was performed in the zero-gravity conditions of an orbiting satellite to minimize pressure differences in the sample. This experimental value of α agrees with theoretical predictions based on variational perturbation theory.

For 0 < α < 1, the heat capacity diverges at the transition temperature (though, since α < 1, the enthalpy stays finite). An example of such behavior is the 3D ferromagnetic phase transition. In the three-dimensional Ising model for uniaxial magnets, detailed theoretical studies have yielded the exponent α ≈ +0.110.

Some model systems do not obey a power-law behavior. For example, mean field theory predicts a finite discontinuity of the heat capacity at the transition temperature, and the two-dimensional Ising model has a logarithmic divergence. However, these systems are limiting cases and an exception to the rule. Real phase transitions exhibit power-law behavior.

Several other critical exponents, β, γ, δ, ν, and η, are defined, examining the power law behavior of a measurable physical quantity near the phase transition. Exponents are related by scaling relations, such as
 * $$\beta = \gamma / (\delta - 1),\quad \nu = \gamma / (2 - \eta).$$

It can be shown that there are only two independent exponents, e.g. ν and η.

It is a remarkable fact that phase transitions arising in different systems often possess the same set of critical exponents. This phenomenon is known as universality. For example, the critical exponents at the liquid–gas critical point have been found to be independent of the chemical composition of the fluid.

More impressively, but understandably from above, they are an exact match for the critical exponents of the ferromagnetic phase transition in uniaxial magnets. Such systems are said to be in the same universality class. Universality is a prediction of the renormalization group theory of phase transitions, which states that the thermodynamic properties of a system near a phase transition depend only on a small number of features, such as dimensionality and symmetry, and are insensitive to the underlying microscopic properties of the system. Again, the divergence of the correlation length is the essential point.

Critical phenomena
There are also other critical phenomena; e.g., besides static functions there is also critical dynamics. As a consequence, at a phase transition one may observe critical slowing down or speeding up. Connected to the previous phenomenon is also the phenomenon of enhanced fluctuations before the phase transition, as a consequence of lower degree of stability of the initial phase of the system. The large static universality classes of a continuous phase transition split into smaller dynamic universality classes. In addition to the critical exponents, there are also universal relations for certain static or dynamic functions of the magnetic fields and temperature differences from the critical value.

Phase transitions in biological systems
Phase transitions play many important roles in biological systems. Examples include the lipid bilayer formation, the coil-globule transition in the process of protein folding and DNA melting, liquid crystal-like transitions in the process of DNA condensation, and cooperative ligand binding to DNA and proteins with the character of phase transition.

In biological membranes, gel to liquid crystalline phase transitions play a critical role in physiological functioning of biomembranes. In gel phase, due to low fluidity of membrane lipid fatty-acyl chains, membrane proteins have restricted movement and thus are restrained in exercise of their physiological role. Plants depend critically on photosynthesis by chloroplast thylakoid membranes which are exposed cold environmental temperatures. Thylakoid membranes retain innate fluidity even at relatively low temperatures because of high degree of fatty-acyl disorder allowed by their high content of linolenic acid, 18-carbon chain with 3-double bonds. Gel-to-liquid crystalline phase transition temperature of biological membranes can be determined by many techniques including calorimetry, fluorescence, spin label electron paramagnetic resonance and NMR by recording measurements of the concerned parameter by at series of sample temperatures. A simple method for its determination from 13-C NMR line intensities has also been proposed.

It has been proposed that some biological systems might lie near critical points. Examples include neural networks in the salamander retina, bird flocks gene expression networks in Drosophila, and protein folding. However, it is not clear whether or not alternative reasons could explain some of the phenomena supporting arguments for criticality. It has also been suggested that biological organisms share two key properties of phase transitions: the change of macroscopic behavior and the coherence of a system at a critical point. Phase transitions are prominent feature of motor behavior in biological systems. Spontaneous gait transitions, as well as fatigue-induced motor task disengagements, show typical critical behavior as an intimation of the sudden qualitative change of the previously stable motor behavioral pattern.

The characteristic feature of second order phase transitions is the appearance of fractals in some scale-free properties. It has long been known that protein globules are shaped by interactions with water. There are 20 amino acids that form side groups on protein peptide chains range from hydrophilic to hydrophobic, causing the former to lie near the globular surface, while the latter lie closer to the globular center. Twenty fractals were discovered in solvent associated surface areas of > 5000 protein segments. The existence of these fractals proves that proteins function near critical points of second-order phase transitions. In groups of organisms in stress (when approaching critical transitions), correlations tend to increase, while at the same time, fluctuations also increase. This effect is supported by many experiments and observations of groups of people, mice, trees, and grassy plants.

Phase transitions in social systems
Phase transitions have been hypothesised to occur in social systems viewed as dynamical systems. A hypothesis proposed in the 1990s and 2000s in the context of peace and armed conflict is that when a conflict that is non-violent shifts to a phase of armed conflict, this is a phase transition from latent to manifest phases within the dynamical system.

Experimental
A variety of methods are applied for studying the various effects. Selected examples are:
 * Thermogravimetry (very common)
 * X-ray diffraction
 * Neutron diffraction
 * Raman Spectroscopy
 * SQUID (measurement of magnetic transitions)
 * Hall effect (measurement of magnetic transitions)
 * Mössbauer spectroscopy (simultaneous measurement of magnetic and non-magnetic transitions. Limited up to about 800–1000 °C)
 * Perturbed angular correlation (simultaneous measurement of magnetic and non-magnetic transitions. No temperature limits. Over 2000 °C already performed, theoretical possible up to the highest crystal material, such as tantalum hafnium carbide 4215 °C.)

title: Phase transition


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Etemenanki

Etemenanki was a ziggurat dedicated to the Mesopotamian god Marduk in the ancient city of Babylon. It now exists only in ruins, located about 90 km south of Baghdad, Iraq. Many scholars have identified Etemenanki as a likely inspiration for the biblical story of the Tower of Babel.

Construction
It is unclear when Etemenanki was originally constructed. Andrew R. George says that it was constructed sometime between the 14th and the 9th century BCE. He argues as follows: The reference to a ziqqurrat at Babylon in the Creation Epic (Enûma Eliš· VI 63: George 1992: 301–2) is more solid evidence, ... for a Middle Assyrian piece of this poem survives to prove the long-held theory that it existed already in the second millennium BC. There is no reason to doubt that this ziqqurrat, described as ziqqurrat apsî elite, "the upper ziqqurrat of the Apsû", was [Etemenanki].

Babylon was destroyed in 689 BCE by Sennacherib, who claims to have destroyed the Etemenanki. It took 88 years to restore the city; work was started by the Assyrian king Esarhaddon, and continued under Nabopolassar followed by his son Nebuchadnezzar II who rebuilt the ziggurat. The city's central feature was the temple of Marduk (Esagila), with which the Etemenanki ziggurat was associated.

Fenollós et al. note that, "The 'Tower of Babel' was not built in a single moment, but rather was the result of a complex history of successive constructions, destruction and reconstruction. Its origin dates back to the reign of Hammurabi and continues to this day with its inevitable and definitive destruction." (Translated from the Italian). The "Tower" as discussed in ancient sources refers to the monument as it appeared in the Neo-Babylonian period.

Descriptions
A Neo-Babylonian royal inscription of Nebuchadnezzar II on a stele from Babylon, claimed to have been found in the 1917 excavation by Robert Koldewey, and of uncertain authenticity, reads: "Etemenanki Zikkurat Babibli [Ziggurat of Babylon] I made it, the wonder of the people of the world, I raised its top to heaven, made doors for the gates, and I covered it with bitumen and bricks." The building is depicted in shallow relief, showing its high first stages with paired flights of steps, five further stepped stages and the temple that surmounted the structure. A floor plan is also shown, depicting the buttressed outer walls and the inner chambers surrounding the central cella.

Foundation cylinders with inscriptions from Nabopolassar were found in the 1880s, two survive, one of which reads: "At that time my lord Marduk told me in regard to E-temen-anki, the ziqqurrat of Babylon, which before my day was (already) very weak and badly buckled, to ground its bottom on the breast of the netherworld, to make its top vie with the heavens. I fashioned mattocks, spades and brick-moulds from ivory, ebony, and musukkannu-wood, and set them in the hands of a vast workforce levied from my land. I had them shape mud bricks without number and mould-baked bricks like countless raindrops. I had the River Arahtu bear asphalt and bitumen like a mighty flood. Through the sagacity of Ea, through the intelligence of Marduk, through the wisdom of Nabû and Nissaba, by means of the vast mind that the god who created me let me possess, I deliberated with my great intellect, I commissioned the wisest experts and the surveyor established the dimensions with the twelve-cubit rule. The master-builders drew taut the measuring cords, they determined the limits. I sought confirmation by consulting Samas, Adad and Marduk and, whenever my mind deliberated (and) I pondered (unsure of) the dimensions, the great gods made (the truth) known to me by the procedure of (oracular) confirmation. Through the craft of exorcism, the wisdom of Ea and Marduk, I purified that place and made firm its foundation platform on its ancient base. In its foundations I laid out gold, silver, gemstones from mountain and sea. Under the brickwork, I set heaps of shining sapsu, sweet-scented oil, aromatics and red earth. I fashioned representations of my royal likeness bearing a soil-basket and positioned (them) variously in the foundation platform. I bowed my neck to my lord Marduk. I rolled up my garment, my kingly robe, and carried on my head bricks and earth (i.e. mud bricks). I had soil-baskets made of gold and silver and made Nebuchadnezzar, my firstborn son, beloved of my heart, carry alongside my workmen earth mixed with wine, oil and resin-chips. I made Nabûsumilisir, his brother, a boy, issue of my body, my darling younger son, take up mattock and spade. I burdened him with a soil-basket of gold and silver and bestowed him on my lord Marduk as a gift.I constructed the building, the replica of E-sarra, in joy and jubilation and raised its top as high as a mountain. For my lord Marduk I made it an object fitting for wonder, just as it was in former times."

In 2011 scholars discovered in the Schøyen Collection the oldest known representation of the Etemenanki. Carved on a black stone, the Tower of Babel Stele, as it is known, dates to 604–562 BCE, the time of Nebuchadnezzar II.

The Etemenanki is described in a cuneiform tablet from Uruk from 229 BCE, a copy of an older text (now in the Louvre, Paris and referred to as the "Esagila" tablet). Translated in 1876 by Assyriologist George Smith, it gives the height of the tower as seven stocks (91 meters) with a square base of 91 meters on each side. This mudbrick structure was confirmed by excavations conducted by Robert Koldewey after 1913. Large stairs were discovered at the south side of the building, where a triple gate connected it with the Esagila. A larger gate to the east connected the Etemenanki with the sacred procession road (now reconstructed in the Pergamon Museum, Berlin).

Until the first translation of the "Esagila" tablet, details of Babylon's ziggurat were known only from the ancient Greek historian Herodotus, who wrote in the mid-5th century BCE: "The center of each division of the town was occupied by a fortress. In the one stood the palace of the kings, surrounded by a wall of great strength and size: in the other was the sacred precinct of Jupiter [Zeus] Belus, a square enclosure two furlongs [402 m] each way, with gates of solid brass; which was also remaining in my time. In the middle of the precinct there was a tower of solid masonry, a furlong [201 m] in length and breadth, upon which was raised a second tower, and on that a third, and so on up to eight. The ascent to the top is on the outside, by a path which winds round all the towers. When one is about half-way up, one finds a resting-place and seats, where persons can sit for some time on their way to the summit. On the topmost tower there is a spacious temple, and inside the temple stands a couch of unusual size, richly adorned, with a golden table by its side. There is no statue of any kind set up in the place, nor is the chamber occupied of nights by any one but a single native woman, who, as the Chaldeans [i.e. the Babylonians], the priests of this god, affirm, is chosen for himself by the deity out of all the women of the land."

This Tower of Jupiter Belus is believed to refer to the Akkadian god Bel, whose name has been Hellenised by Herodotus to Zeus Belus. It is likely that it corresponds to Etemenanki. Herodotus does not say that he visited Babylon or the ziggurat, however; the account contains multiple inaccuracies and is most likely second hand.

Final demolition
In 331 BCE, Alexander the Great captured Babylon and ordered repairs to the Etemenanki. When Alexander returned to the ancient city in 323 BCE, he noted that no progress had been made, and ordered his army to demolish the entire building in order to prepare a final rebuilding. His death, however, prevented the reconstruction. The Babylonian Chronicles and Astronomical Diaries record several attempts to rebuild the Etemenanki, which were always preceded by removing the last debris of the original ziggurat. The Ruin of Esagila Chronicle mentions that the Seleucid crown prince Antiochus I decided to rebuild it and made a sacrifice in preparation. However, while there, he stumbled on the rubble and fell. He then angrily ordered his elephant drivers to destroy the last of the remains. There are no later references to the Etemenanki from antiquity.

Modern hypotheses regarding height
Modern scholars dispute the claim by the ancient Babylonian source (the "Esagila" tablet) that the Etemenanki was 91 meters tall. "[The modern] interpretation of Esagil's text raises a serious technical problem: the excessive height of the first two terraces of the ziggurat and the total height of the building defy the laws of statics and compressive strength of a material such as raw earth brick.” (Translated from the Italian)."Even allowing variation in the design of a six-level terraced structure, at that height, the compression stress on the structure would be somewhere around two to three times as much as comparable structures of the same time period. Fenollós et al. propose that, assuming the structure did indeed use a six-level terrace design as depicted in the Tower of Babel stele, the ziggurat was probably closer to 54 meters tall. The temple at the top contributed another 12 meters in height, for a total height of 66 meters.

In popular culture
In the Portugal Pack of the video game Civilization VI, Etemenanki was introduced as one of the wonders in the game.

In the Lucasarts PC video game Indiana Jones and the Infernal Machine, Etemenanki is a key location, eventually revealed to have been both the biblical Tower of Babel and a temple to the god Marduk.

title: Etemenanki