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IRC

IRC (Internet Relay Chat) is a text-based chat system for instant messaging. IRC is designed for group communication in discussion forums, called channels, but also allows one-on-one communication via private messages as well as chat and data transfer, including file sharing.

Internet Relay Chat is implemented as an application layer protocol to facilitate communication in the form of text. The chat process works on a client–server networking model. Users connect, using a clientwhich may be a web app, a standalone desktop program, or embedded into part of a larger programto an IRC server, which may be part of a larger IRC network. Examples of programs used to connect include Mibbit, IRCCloud, KiwiIRC, and mIRC.

IRC usage has been declining steadily since 2003, losing 60 percent of its users. In April 2011, the top 100 IRC networks served more than 200,000 users at a time.

History
IRC was created by Jarkko Oikarinen in August 1988 to replace a program called MUT (MultiUser Talk) on a BBS called OuluBox at the University of Oulu in Finland, where he was working at the Department of Information Processing Science. Jarkko intended to extend the BBS software he administered, to allow news in the Usenet style, real time discussions and similar BBS features. The first part he implemented was the chat part, which he did with borrowed parts written by his friends Jyrki Kuoppala and Jukka Pihl. The first IRC network was running on a single server named tolsun.oulu.fi. Oikarinen found inspiration in a chat system known as Bitnet Relay, which operated on the BITNET.

Jyrki Kuoppala pushed Oikarinen to ask Oulu University to free the IRC code so that it also could be run outside of Oulu, and after they finally got it released, Jyrki Kuoppala immediately installed another server. This was the first "IRC network". Oikarinen got some friends at the Helsinki University and Tampere University to start running IRC servers when his number of users increased and other universities soon followed. At this time Oikarinen realized that the rest of the BBS features probably would not fit in his program.

Oikarinen contacted people at the University of Denver and Oregon State University. They had their own IRC network running and wanted to connect to the Finnish network. They had obtained the program from one of Oikarinen's friends, Vijay Subramaniam—the first non-Finnish person to use IRC. IRC then grew larger and got used on the entire Finnish national network—FUNET—and then connected to Nordunet, the Scandinavian branch of the Internet. In November 1988, IRC had spread across the Internet and in the middle of 1989, there were some 40 servers worldwide.

EFnet
In August 1990, the first major disagreement took place in the IRC world. The "A-net" (Anarchy net) included a server named eris.berkeley.edu. It was all open, required no passwords and had no limit on the number of connects. As Greg "wumpus" Lindahl explains: "it had a wildcard server line, so people were hooking up servers and nick-colliding everyone". The "Eris Free Network", EFnet, made the eris machine the first to be Q-lined (Q for quarantine) from IRC. In wumpus' words again: "Eris refused to remove that line, so I formed EFnet. It wasn't much of a fight; I got all the hubs to join, and almost everyone else got carried along." A-net was formed with the eris servers, while EFnet was formed with the non-eris servers. History showed most servers and users went with EFnet. Once A-net disbanded, the name EFnet became meaningless, and once again it was the one and only IRC network.

Around that time IRC was used to report on the 1991 Soviet coup d'état attempt throughout a media blackout. It was previously used in a similar fashion during the Gulf War. Chat logs of these and other events are kept in the ibiblio archive.

Undernet fork
Another fork effort, the first that made a lasting difference, was initiated by "Wildthang" in the United States in October 1992. (It forked off the EFnet ircd version 2.8.10). It was meant to be just a test network to develop bots on but it quickly grew to a network "for friends and their friends". In Europe and Canada a separate new network was being worked on and in December the French servers connected to the Canadian ones, and by the end of the month, the French and Canadian network was connected to the US one, forming the network that later came to be called "The Undernet".

The "undernetters" wanted to take ircd further in an attempt to make it use less bandwidth and to try to sort out the channel chaos (netsplits and takeovers) that EFnet started to suffer from. For the latter purpose, the Undernet implemented timestamps, new routing and offered the CService—a program that allowed users to register channels and then attempted to protect them from troublemakers. The first server list presented, from 15 February 1993, includes servers from the U.S., Canada, France, Croatia and Japan. On 15 August, the new user count record was set to 57 users.

In May 1993, RFC 1459 was published and details a simple protocol for client/server operation, channels, one-to-one and one-to-many conversations. A significant number of extensions like CTCP, colors and formats are not included in the protocol specifications, nor is character encoding, which led various implementations of servers and clients to diverge. Software implementation varied significantly from one network to the other, each network implementing their own policies and standards in their own code bases.

DALnet fork
During the summer of 1994, the Undernet was itself forked. The new network was called DALnet (named after its founder: dalvenjah), formed for better user service and more user and channel protections. One of the more significant changes in DALnet was use of longer nicknames (the original ircd limit being 9 letters). DALnet ircd modifications were made by Alexei "Lefler" Kosut. DALnet was thus based on the Undernet ircd server, although the DALnet pioneers were EFnet abandoners. According to James Ng, the initial DALnet people were "ops in #StarTrek sick from the constant splits/lags/takeovers/etc".

DALnet quickly offered global WallOps (IRCop messages that can be seen by users who are +w (/mode NickName +w)), longer nicknames, Q:Lined nicknames (nicknames that cannot be used i.e. ChanServ, IRCop, NickServ, etc.), global K:Lines (ban of one person or an entire domain from a server or the entire network), IRCop only communications: GlobOps, +H mode showing that an IRCop is a "helpop" etc. Much of DALnet's new functions were written in early 1995 by Brian "Morpher" Smith and allow users to own nicknames, control channels, send memos, and more.

IRCnet fork
In July 1996, after months of flame wars and discussions on the mailing list, there was yet another split due to disagreement in how the development of the ircd should evolve. Most notably, the "European" (most of those servers were in Europe) side that later named itself IRCnet argued for nick and channel delays whereas the EFnet side argued for timestamps. There were also disagreements about policies: the European side had started to establish a set of rules directing what IRCops could and could not do, a point of view opposed by the US side.

Most (not all) of the IRCnet servers were in Europe, while most of the EFnet servers were in the US. This event is also known as "The Great Split" in many IRC societies. EFnet has since (as of August 1998) grown and passed the number of users it had then. In the (northern) autumn of the year 2000, EFnet had some 50,000 users and IRCnet 70,000.

Modern IRC
IRC has changed much over its life on the Internet. New server software has added a multitude of new features.
 * Services: Network-operated bots to facilitate registration of nicknames and channels, sending messages for offline users and network operator functions.
 * Extra modes: While the original IRC system used a set of standard user and channel modes, new servers add many new modes for features such as removing color codes from text, or obscuring a user's hostmask ("cloaking") to protect from denial-of-service attacks.
 * Proxy detection: Most modern servers support detection of users attempting to connect through an insecure (misconfigured or exploited) proxy server, which can then be denied a connection. This proxy detection software is used by several networks, although that real time list of proxies is defunct since early 2006.
 * Additional commands: New commands can be such things as shorthand commands to issue commands to Services, to network-operator-only commands to manipulate a user's hostmask.
 * Encryption: For the client-to-server leg of the connection TLS might be used (messages cease to be secure once they are relayed to other users on standard connections, but it makes eavesdropping on or wiretapping an individual's IRC sessions difficult). For client-to-client communication, SDCC (Secure DCC) can be used.
 * Connection protocol: IRC can be connected to via IPv4, the old version of the Internet Protocol, or by IPv6, the current standard of the protocol.

, a new standardization effort is under way under a working group called IRCv3, which focuses on more advanced client features such as instant notifications, better history support and improved security. , no major IRC networks have fully adopted the proposed standard.

there are 481 different IRC networks known to be operating, of which the open source Libera Chat, founded in May 2021, has the most users, with 20,374 channels on 26 servers; between them, the top 100 IRC networks share over 100 thousand channels operating on about one thousand servers.

After its golden era during the 1990s and early 2000s (240,000 users on QuakeNet in 2004), IRC has seen a significant decline, losing around 60% of users between 2003 and 2012, with users moving to social media platforms such as Facebook or Twitter, but also to open platforms such as XMPP which was developed in 1999. Certain networks such as Freenode have not followed the overall trend and have more than quadrupled in size during the same period. However, Freenode, which in 2016 had around 90,000 users, has since declined to about 9,300 users.

The largest IRC networks have traditionally been grouped as the "Big Four"   —a designation for networks that top the statistics. The Big Four networks change periodically, but due to the community nature of IRC there are a large number of other networks for users to choose from.

Historically the "Big Four" were:
 * EFnet
 * IRCnet
 * Undernet
 * DALnet

IRC reached 6 million simultaneous users in 2001 and 10 million users in 2004–2005, dropping to around 350k in 2021.

The top 100 IRC networks have around 230k users connected at peak hours.

Timeline
Timeline of major servers:
 * EFnet, 1990 to present
 * Undernet, 1992 to present
 * DALnet, 1994 to present
 * freenode, 1995 to present
 * IRCnet, 1996 to present
 * QuakeNet, 1997 to present
 * Open and Free Technology Community, 2001 to present
 * Rizon, 2002 to present
 * Libera Chat, 2021 to present

Technical information
IRC is an open protocol that uses TCP and, optionally, TLS. An IRC server can connect to other IRC servers to expand the IRC network. Users access IRC networks by connecting a client to a server. There are many client implementations, such as mIRC, HexChat and irssi, and server implementations, e.g. the original IRCd. Most IRC servers do not require users to register an account but a nickname is required before being connected.

IRC was originally a plain text protocol (although later extended), which on request was assigned port 194/TCP by IANA. However, the de facto standard has always been to run IRC on 6667/TCP and nearby port numbers (for example TCP ports 6660–6669, 7000) to avoid having to run the IRCd software with root privileges.

The protocol specified that characters were 8-bit but did not specify the character encoding the text was supposed to use. This can cause problems when users using different clients and/or different platforms want to converse.

All client-to-server IRC protocols in use today are descended from the protocol implemented in the irc2.4.0 version of the IRC2 server, and documented in RFC 1459. Since RFC 1459 was published, the new features in the irc2.10 implementation led to the publication of several revised protocol documents (RFC 2810, RFC 2811, RFC 2812 and RFC 2813); however, these protocol changes have not been widely adopted among other implementations.

Although many specifications on the IRC protocol have been published, there is no official specification, as the protocol remains dynamic. Virtually no clients and very few servers rely strictly on the above RFCs as a reference.

Microsoft made an extension for IRC in 1998 via the proprietary IRCX. They later stopped distributing software supporting IRCX, instead developing the proprietary MSNP.

The standard structure of a network of IRC servers is a tree. Messages are routed along only necessary branches of the tree but network state is sent to every server and there is generally a high degree of implicit trust between servers. However, this architecture has a number of problems. A misbehaving or malicious server can cause major damage to the network and any changes in structure, whether intentional or a result of conditions on the underlying network, require a net-split and net-join. This results in a lot of network traffic and spurious quit/join messages to users and temporary loss of communication to users on the splitting servers. Adding a server to a large network means a large background bandwidth load on the network and a large memory load on the server. Once established, however, each message to multiple recipients is delivered in a fashion similar to multicast, meaning each message travels a network link exactly once. This is a strength in comparison to non-multicasting protocols such as Simple Mail Transfer Protocol (SMTP) or Extensible Messaging and Presence Protocol (XMPP).

An IRC daemon can be used on a local area network (LAN). IRC can thus be used to facilitate communication between people within the local area network (internal communication).

Commands and replies
IRC has a line-based structure. Clients send single-line messages to the server, receive replies to those messages and receive copies of some messages sent by other clients. In most clients, users can enter commands by prefixing them with a '/'. Depending on the command, these may either be handled entirely by the client, or (generally for commands the client does not recognize) passed directly to the server, possibly with some modification.

Due to the nature of the protocol, automated systems cannot always correctly pair a sent command with its reply with full reliability and are subject to guessing.

Channels
The basic means of communicating to a group of users in an established IRC session is through a channel. Channels on a network can be displayed using the IRC command LIST, which lists all currently available channels that do not have the modes +s or +p set, on that particular network.

Users can join a channel using the JOIN command, in most clients available as /join #channelname. Messages sent to the joined channels are then relayed to all other users.

Channels that are available across an entire IRC network are prefixed with a '#', while those local to a server use '&'. Other less common channel types include '+' channels—'modeless' channels without operators —and '!' channels, a form of timestamped channel on normally non-timestamped networks.

Modes
Users and channels may have modes that are represented by individual case-sensitive letters and are set using the MODE command. User modes and channel modes are separate and can use the same letter to mean different things (e.g. user mode "i" is invisible mode while channel mode "i" is invite only. ) Modes are usually set and unset using the mode command that takes a target (user or channel), a set of modes to set (+) or unset (-) and any parameters the modes need.

Some channel modes take parameters and other channel modes apply to a user on a channel or add or remove a mask (e.g. a ban mask) from a list associated with the channel rather than applying to the channel as a whole. Modes that apply to users on a channel have an associated symbol that is used to represent the mode in names replies (sent to clients on first joining a channel and use of the names command) and in many clients also used to represent it in the client's displayed list of users in a channel or to display an own indicator for a user's modes.

In order to correctly parse incoming mode messages and track channel state the client must know which mode is of which type and for the modes that apply to a user on a channel which symbol goes with which letter. In early implementations of IRC this had to be hard-coded in the client but there is now a de facto standard extension to the protocol called ISUPPORT that sends this information to the client at connect time using numeric 005.

There is a small design fault in IRC regarding modes that apply to users on channels: the names message used to establish initial channel state can only send one such mode per user on the channel, but multiple such modes can be set on a single user. For example, if a user holds both operator status (+o) and voice status (+v) on a channel, a new client will be unable to see the mode with less priority (i.e. voice). Workarounds for this are possible on both the client and server side; a common solution is to use IRCv3 "multi-prefix" extension.

Standard (RFC 1459) modes
Many daemons and networks have added extra modes or modified the behavior of modes in the above list.

Channel operators
A channel operator is a client on an IRC channel that manages the channel. IRC channel operators can be easily seen by the symbol or icon next to their name (varies by client implementation, commonly a "@" symbol prefix, a green circle, or a Latin letter "+o"/"o"). On most networks, an operator can:
 * Kick a user.
 * Ban a user.
 * Give another user IRC Channel Operator Status or IRC Channel Voice Status.
 * Change the IRC Channel topic while channel mode +t is set.
 * Change the IRC Channel Mode locks.

Operators
There are also users who maintain elevated rights on their local server, or the entire network; these are called IRC operators, sometimes shortened to IRCops or Opers (not to be confused with channel operators). As the implementation of the IRCd varies, so do the privileges of the IRC operator on the given IRCd. RFC 1459 claims that IRC operators are "a necessary evil" to keep a clean state of the network, and as such they need to be able to disconnect and reconnect servers. Additionally, to prevent malicious users or even harmful automated programs from entering IRC, IRC operators are usually allowed to disconnect clients and completely ban IP addresses or complete subnets. Networks that carry services (NickServ et al.) usually allow their IRC operators also to handle basic "ownership" matters. Further privileged rights may include overriding channel bans (being able to join channels they would not be allowed to join, if they were not opered), being able to op themselves on channels where they would not be able without being opered, being auto-opped on channels always and so forth.

Hostmasks
A hostmask is a unique identifier of an IRC client connected to an IRC server. IRC servers, services, and other clients, including bots, can use it to identify a specific IRC session.

The format of a hostmask is. The hostmask looks similar to, but should not be confused with an e-mail address.

The nick part is the nickname chosen by the user and may be changed while connected. The user part is the username reported by ident on the client. If ident is not available on the client, the username specified when the client connected is used after being prefixed with a tilde.

The host part is the hostname the client is connecting from. If the IP address of the client cannot be resolved to a valid hostname by the server, it is used instead of the hostname.

Because of the privacy implications of exposing the IP address or hostname of a client, some IRC daemons also provide privacy features, such as InspIRCd or UnrealIRCd's "+x" mode. This hashes a client IP address or masks part of a client's hostname, making it unreadable to users other than IRCops. Users may also have the option of requesting a "virtual host" (or "vhost"), to be displayed in the hostmask to allow further anonymity. Some IRC networks, such as Libera Chat or Freenode, use these as "cloaks" to indicate that a user is affiliated with a group or project.

URI scheme
There are three provisional recognized uniform resource identifier (URI) schemes for Internet Relay Chat:,  , and. When supported, they allow hyperlinks of various forms, including irc:// [: ]/[ [?]] ircs:// [: ]/[ [?]] irc6:// [: ]/[ [?]] (where items enclosed within brackets ([,]) are optional) to be used to (if necessary) connect to the specified host (or network, if known to the IRC client) and join the specified channel. (This can be used within the client itself, or from another application such as a Web browser). irc is the default URI, irc6 specifies a connection to be made using IPv6, and ircs specifies a secure connection.

Per the specification, the usual hash symbol (#) will be prepended to channel names that begin with an alphanumeric character—allowing it to be omitted. Some implementations (for example, mIRC) will do so unconditionally resulting in a (usually unintended) extra (for example, ##channel), if included in the URL.

Some implementations allow multiple channels to be specified, separated by commas.

Challenges
Issues in the original design of IRC were the amount of shared state data being a limitation on its scalability, the absence of unique user identifications leading to the nickname collision problem, lack of protection from netsplits by means of cyclic routing,  the trade-off in scalability for the sake of real-time user presence information, protocol weaknesses providing a platform for abuse, no transparent and optimizable message passing, and no encryption. Some of these issues have been addressed in Modern IRC.

Attacks
Because IRC connections may be unencrypted and typically span long time periods, they are an attractive target for DoS/DDoS attackers and hackers. Because of this, careful security policy is necessary to ensure that an IRC network is not susceptible to an attack such as a takeover war. IRC networks may also K-line or G-line users or servers that have a harming effect.

Some IRC servers support SSL/TLS connections for security purposes. This helps stop the use of packet sniffer programs to obtain the passwords of IRC users, but has little use beyond this scope due to the public nature of IRC channels. SSL connections require both client and server support (that may require the user to install SSL binaries and IRC client specific patches or modules on their computers). Some networks also use SSL for server-to-server connections, and provide a special channel flag (such as ) to only allow SSL-connected users on the channel, while disallowing operator identification in clear text, to better utilize the advantages that SSL provides.

IRC served as an early laboratory for many kinds of Internet attacks, such as using fake ICMP unreachable messages to break TCP-based IRC connections (nuking) to annoy users or facilitate takeovers.

Abuse prevention
One of the most contentious technical issues surrounding IRC implementations, which survives to this day, is the merit of "Nick/Channel Delay" vs. "Timestamp" protocols. Both methods exist to solve the problem of denial-of-service attacks, but take very different approaches. The problem with the original IRC protocol as implemented was that when two servers split and rejoined, the two sides of the network would simply merge their channels. If a user could join on a "split" server, where a channel that existed on the other side of the network was empty, and gain operator status, they would become a channel operator of the "combined" channel after the netsplit ended; if a user took a nickname that existed on the other side of the network, the server would kill both users when rejoining (a "nick collision"). This was often abused to "mass-kill" all users on a channel, thus creating "opless" channels where no operators were present to deal with abuse. Apart from causing problems within IRC, this encouraged people to conduct denial-of-service attacks against IRC servers in order to cause netsplits, which they would then abuse.

The nick delay (ND) and channel delay (CD) strategies aim to prevent abuse by delaying reconnections and renames. After a user signs off and the nickname becomes available, or a channel ceases to exist because all its users parted (as often happens during a netsplit), the server will not allow any user to use that nickname or join that channel, until a certain period of time (the delay) has passed. The idea behind this is that even if a netsplit occurs, it is useless to an abuser because they cannot take the nickname or gain operator status on a channel, and thus no collision of a nickname or "merging" of a channel can occur. To some extent, this inconveniences legitimate users, who might be forced to briefly use a different name after rejoining (appending an underscore is popular).

The timestamp protocol is an alternative to nick/channel delays which resolves collisions using timestamped priority. Every nickname and channel on the network is assigned a timestamp – the date and time when it was created. When a netsplit occurs, two users on each side are free to use the same nickname or channel, but when the two sides are joined, only one can survive. In the case of nicknames, the newer user, according to their TS, is killed; when a channel collides, the members (users on the channel) are merged, but the channel operators on the "losing" side of the split lose their channel operator status.

TS is a much more complicated protocol than ND/CD, both in design and implementation, and despite having gone through several revisions, some implementations still have problems with "desyncs" (where two servers on the same network disagree about the current state of the network), and allowing too much leniency in what was allowed by the "losing" side. Under the original TS protocols, for example, there was no protection against users setting bans or other modes in the losing channel that would then be merged when the split rejoined, even though the users who had set those modes lost their channel operator status. Some modern TS-based IRC servers have also incorporated some form of ND and/or CD in addition to timestamping in an attempt to further curb abuse.

Most networks today use the timestamping approach. The timestamp versus ND/CD disagreements caused several servers to split away from EFnet and form the newer IRCnet. After the split, EFnet moved to a TS protocol, while IRCnet used ND/CD.

In recent versions of the IRCnet ircd, as well as ircds using the TS6 protocol (including Charybdis), ND has been extended/replaced by a mechanism called SAVE. This mechanism assigns every client a UID upon connecting to an IRC server. This ID starts with a number, which is forbidden in nicks (although some ircds, namely IRCnet and InspIRCd, allow clients to switch to their own UID as the nickname).

If two clients with the same nickname join from different sides of a netsplit ("nick collision"), the first server to see this collision will force both clients to change their nick to their UID, thus saving both clients from being disconnected. On IRCnet, the nickname will also be locked for some time (ND) to prevent both clients from changing back to the original nickname, thus colliding again.

Client software

Client software exists for various operating systems or software packages, as well as web-based or inside games. Many different clients are available for the various operating systems, including Windows, Unix and Linux, macOS and mobile operating systems (such as iOS and Android). On Windows, mIRC is one of the most popular clients. Some Linux distributions come with an IRC client preinstalled, such as Linux Mint which comes with HexChat preinstalled.

Some programs which are extensible through plug-ins also serve as platforms for IRC clients. For instance, a client called ERC, written entirely in Emacs Lisp, is included in v.22.3 of Emacs. Therefore, any platform that can run Emacs can run ERC.

A number of web browsers have built-in IRC clients, such as: Web-based clients, such as Mibbit and open source KiwiIRC, can run in most browsers.
 * Opera (version 12.18 and earlier) and the
 * ChatZilla add-on for Mozilla Firefox (for Firefox 56 and earlier; included as a built-in component of SeaMonkey).

Games such as War§ow, Unreal Tournament (up to Unreal Tournament 2004), Uplink, Spring Engine-based games, 0 A.D. and ZDaemon have included IRC.

Ustream's chat interface is IRC with custom authentication as well as Twitch's (formerly Justin.tv).

Bots
A typical use of bots in IRC is to provide IRC services or specific functionality within a channel such as to host a chat-based game or provide notifications of external events. However, some IRC bots are used to launch malicious attacks such as denial of service, spamming, or exploitation.

Bouncer
A program that runs as a daemon on a server and functions as a persistent proxy is known as a BNC or bouncer. The purpose is to maintain a connection to an IRC server, acting as a relay between the server and client, or simply to act as a proxy. Should the client lose network connectivity, the BNC may stay connected and archive all traffic for later delivery, allowing the user to resume their IRC session without disrupting their connection to the server.

Furthermore, as a way of obtaining a bouncer-like effect, an IRC client (typically text-based, for example Irssi) may be run on an always-on server to which the user connects via ssh. This also allows devices that only have ssh functionality, but no actual IRC client installed themselves, to connect to the IRC, and it allows sharing of IRC sessions.

To keep the IRC client from quitting when the ssh connection closes, the client can be run inside a terminal multiplexer such as GNU Screen or tmux, thus staying connected to the IRC network(s) constantly and able to log conversation in channels that the user is interested in, or to maintain a channel's presence on the network. Modelled after this setup, in 2004 an IRC client following the client–server, called Smuxi, was launched.

Search engines
There are numerous search engines available to aid the user in finding what they are looking for on IRC. Generally the search engine consists of two parts, a "back-end" (or "spider/crawler") and a front-end "search engine".

The back-end (spider/webcrawler) is the work horse of the search engine. It is responsible for crawling IRC servers to index the information being sent across them. The information that is indexed usually consists solely of channel text (text that is publicly displayed in public channels). The storage method is usually some sort of relational database, like MySQL or Oracle.

The front-end "search engine" is the user interface to the database. It supplies users with a way to search the database of indexed information to retrieve the data they are looking for. These front-end search engines can also be coded in numerous programming languages.

Most search engines have their own spider that is a single application responsible for crawling IRC and indexing data itself; however, others are "user based" indexers. The latter rely on users to install their "add-on" to their IRC client; the add-on is what sends the database the channel information of whatever channels the user happens to be on.

Many users have implemented their own ad hoc search engines using the logging features built into many IRC clients. These search engines are usually implemented as bots and dedicated to a particular channel or group of associated channels.

Character encoding
IRC still lacks a single globally accepted standard convention for how to transmit characters outside the 7-bit ASCII repertoire. IRC servers normally transfer messages from a client to another client just as byte sequences, without any interpretation or recoding of characters. The IRC protocol (unlike e.g. MIME or HTTP) lacks mechanisms for announcing and negotiating character encoding options. This has put the responsibility for choosing the appropriate character codec on the client. In practice, IRC channels have largely used the same character encodings that were also used by operating systems (in particular Unix derivatives) in the respective language communities:
 * 7-bit era: In the early days of IRC, especially among Scandinavian and Finnish language users, national variants of ISO 646 were the dominant character encodings. These encode non-ASCII characters like Ä Ö Å ä ö å at code positions 0x5B 0x5C 0x5D 0x7B 0x7C 0x7D (US-ASCII: [ \ ] { | }). That is why these codes are always allowed in nicknames. According to RFC 1459, { | } in nicknames should be treated as lowercase equivalents of [ \ ] respectively. By the late 1990s, the use of 7-bit encodings had disappeared in favour of ISO 8859-1, and such equivalence mappings were dropped from some IRC daemons.
 * 8-bit era: Since the early 1990s, 8-bit encodings such as ISO 8859-1 have become commonly used for European languages. Russian users had a choice of KOI8-R, ISO 8859-5 and CP1251, and since about 2000, modern Russian IRC networks convert between these different commonly used encodings of the Cyrillic script.
 * Multi-byte era: For a long time, East Asian IRC channels with logographic scripts in China, Japan, and Korea have been using multi-byte encodings such as EUC or ISO-2022-JP. With the common migration from ISO 8859 to UTF-8 on Linux and Unix platforms since about 2002, UTF-8 has become an increasingly popular substitute for many of the previously used 8-bit encodings in European channels. Some IRC clients are now capable of reading messages both in ISO 8859-1 or UTF-8 in the same channel, heuristically autodetecting which encoding is used. The shift to UTF-8 began in particular on Finnish-speaking IRC (Merkistö (Finnish) ).

Today, the UTF-8 encoding of Unicode/ISO 10646 would be the most likely contender for a single future standard character encoding for all IRC communication, if such standard ever relaxed the 510-byte message size restriction. UTF-8 is ASCII compatible and covers the superset of all other commonly used coded character set standards.

File sharing
Much like conventional P2P file sharing, users can create file servers that allow them to share files with each other by using customised IRC bots or scripts for their IRC client. Often users will group together to distribute warez via a network of IRC bots.

Technically, IRC provides no file transfer mechanisms itself; file sharing is implemented by IRC clients, typically using the Direct Client-to-Client (DCC) protocol, in which file transfers are negotiated through the exchange of private messages between clients. The vast majority of IRC clients feature support for DCC file transfers, hence the view that file sharing is an integral feature of IRC. The commonplace usage of this protocol, however, sometimes also causes DCC spam. DCC commands have also been used to exploit vulnerable clients into performing an action such as disconnecting from the server or exiting the client.

title: IRC


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Ideogram

An ideogram or ideograph (from Greek 'idea' +  'to write') is a symbol that represents an idea or concept independent of any particular language. Some ideograms are more arbitrary than others: some are only meaningful assuming preexisting familiarity with some convention; others more directly resemble their signifieds. Ideograms that represent physical objects by visually resembling them are called pictograms.

 * Numerals and mathematical symbols are ideograms, for example ⟨1⟩ 'one', ⟨2⟩ 'two', ⟨+⟩ 'plus', and ⟨=⟩ 'equals'.
 * The ampersand ⟨&⟩ is used in many languages to represent the word and, originally a stylized ligature of the Latin word et.
 * Other typographical examples include ⟨§⟩ 'section', ⟨€⟩ 'euro', ⟨£⟩ 'pound sterling', and ⟨©⟩ 'copyright'.

Ideograms are not to be equated with logograms, which represent specific morphemes in a language. In a broad sense, ideograms may form part of a writing system otherwise based on other principles, like the examples above in the phonetic English writing system—while also potentially representing the same idea across several languages, as they do not correspond to a specific spoken word. There may not always be a single way to read a given ideograph. While remaining logograms assigned to morphemes, specific Chinese characters like ⟨⟩ 'middle' may be classified as ideographs in a narrower sense, given their origin and visual structure.

Pictograms and indicatives
Pictograms are ideograms that represent an idea through a direct graphical resemblance to what is being referenced. In proto-writing systems, pictograms generally comprised most of the available symbols. Their use could also be extended via the rebus principle: for example, the pictorial Dongba symbols without Geba annotation cannot represent the Naxi language, but are used as a mnemonic for the recitation of oral literature. Some systems also use indicatives, which denote abstract concepts. Sometimes, the word ideogram is used to refer exclusively to indicatives, contrasting them with pictograms.

The word ideogram has historically often been used to describe Egyptian hieroglyphs, Sumerian cuneiform, and Chinese characters. However, these symbols represent semantic elements of a language, and not the underlying ideas directly—their use generally requires knowledge of a specific spoken language. Modern scholars refer to these symbols instead as logograms, and generally avoid calling them ideograms. Most logograms include some representation of the pronunciation of the corresponding word in the language, often using the rebus principle. Later systems used selected symbols to represent the sounds of the language, such as the adaptation of the logogram for 'ox' as the letter aleph representing the initial glottal stop. However, some logograms still meaningfully depict the meaning of the morpheme they represent visually. Pictograms are shaped like the object that the word refers to, such as an icon of a bull denoting the Semitic word 'ox'. Other logograms may visually represent meaning via more abstract techniques.

Many Egyptian hieroglyphs and cuneiform graphs could be used either logographically or phonetically. For example, the Sumerian dingir $⟨⟩$ could represent the word 'deity', the god An or the word  'sky'. In Akkadian, the graph $⟨Assyrian cuneiform U1202D MesZL 10.svg⟩$ could represent the stem 'deity', the word   'sky', or the syllable.

While Chinese characters generally function as logograms, three of the six classes in the traditional classification are ideographic (or semantographic) in origin, as they have no phonetic component:
 * Pictograms are generally among the oldest characters, with forms dating to the 12th century BC. Generally, with the evolution of the script, the forms of pictographs became less directly representational, to the extent that their referents are no longer plausible to intuit. Examples include $⟨⟩$ 'field'，and $⟨⟩$ 'heart'.
 * Indicatives like $⟨⟩$ 'up' and $⟨⟩$ 'down', or numerals like $⟨⟩$ 'three'.
 * Ideographic compounds have a meaning synthesized from several other characters, such as $⟨⟩$ 'bright', a compound of $⟨⟩$ 'Sun' and $⟨⟩$ 'Moon', or $⟨⟩$ 'rest', composed of $⟨⟩$ 'person' and $⟨⟩$ 'tree'. As the understanding of Old Chinese phonology developed during the second half of the 20th century, many researchers became convinced that the etymology of most characters originally thought to be ideographic compounds actually included some phonetic component.

Example of ideograms are the DOT pictograms, a collection of 50 symbols developed during the 1970s by the American Institute of Graphic Arts at the request of the United States Department of Transportation. Initially used to mark airports, the system gradually became more widespread.

Pure signs
Many ideograms only represent ideas by convention. For example, a red octagon only carries the meaning of 'stop' due to the public association and reification of that meaning over time. In the field of semiotics, these are a type of pure sign, a term which also includes symbols using non-graphical media. Modern analysis of Chinese characters reveals that pure signs are as old as the system itself, with prominent examples including the numerals representing numbers larger than four, including $⟨⟩$ 'five', and $⟨⟩$ 'eight'. These do not indicate anything about the quantities they represent visually or phonetically, only conventionally.

Mathematical notation
A mathematical symbol is a type of ideogram.

History
As true writing systems emerged from systems of pure ideograms, later societies with phonetic writing were often compelled by the intuitive connection between pictures, diagrams and logograms—though ultimately ignorant of the latter's necessary phonetic dimension. Greek speakers began regularly visiting Egypt during the 7th century BC. Ancient Greek writers generally mistook the Egyptian writing system to be purely ideographic. According to tradition, the Greeks had acquired the ability to write, among other things, from the Egyptians through Pythagoras (c. 570), who had been directly taught their silent form of "symbolic teaching". Beginning with Plato (428–347 BC), the conception of hieroglyphs as ideograms was rooted in a broader metaphysical conception of most language as an imperfect and obfuscatory image of reality. The views of Plato involved an ontologically separate world of forms, but those of his student Aristotle (384–322 BC) instead saw the forms as parts identical within the soul of every person. For both, ideography was a more perfect representation of the forms possessed by the Egyptians. The Aristotelian framework would be the foundation for the conception of language in the Mediterranean world into the medieval era.

According to the classical theory, because ideographs directly reflected the forms, they were the only "true language", and had the unique ability to communicate arcane wisdom to readers. The ability to read Egyptian hieroglyphs had been lost during late antiquity, in the context of the country's Hellenization and Christianization. However, the traditional notion that the latter trends compelled the abandonment of hieroglyphic writing has been rejected by recent scholarship.

Europe only became fully acquainted with written Chinese near the end of the 16th century, and initially related the system to their existing framework of ideography as partially informed by Egyptian hieroglyphs. Ultimately, Jean-François Champollion's successful decipherment of hieroglyphs in 1823 stemmed from an understanding that they did represent spoken Egyptian language, as opposed to being purely ideographic. Champollion's insight in part stemmed from his familiarity with the work of French sinologist Jean-Pierre Abel-Rémusat regarding fanqie, which demonstrated that Chinese characters were often used to write sounds, and not just ideas.

Proposed universal languages
Inspired by these conceptions of ideography, several attempts have been made to a design a universal written language—i.e., an ideography whose interpretations are accessible to all people with no regard to the languages they speak. An early proposal was made in 1668 by John Wilkins in An Essay Towards a Real Character, and a Philosophical Language. More recently, Blissymbols was devised by Charles K. Bliss in 1949, and currently includes over 2,000 graphs.

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title: Ideogram


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Irish Republican Army (1919–1922)

The Irish Republican Army (IRA; Óglaigh na hÉireann) was an Irish republican revolutionary paramilitary organisation. The ancestor of many groups also known as the Irish Republican Army, and distinguished from them as the "Old IRA", it was descended from the Irish Volunteers, an organisation established on 25 November 1913 that staged the Easter Rising in April 1916. In 1919, the Irish Republic that had been proclaimed during the Easter Rising was formally established by an elected assembly (Dáil Éireann), and the Irish Volunteers were recognised by Dáil Éireann as its legitimate army. Thereafter, the IRA waged a guerrilla campaign against the British occupation of Ireland in the 1919–1921 Irish War of Independence.

Following the signing in 1921 of the Anglo-Irish Treaty, which ended the War of Independence, a split occurred within the IRA. Members who supported the treaty formed the nucleus of the Irish National Army. However, the majority of the IRA was opposed to the treaty. The anti-treaty IRA fought a civil war against the Free State Army in 1922–1923, with the intention of creating a fully independent all-Ireland republic. Having lost the civil war, this group remained in existence, with the intention of overthrowing the governments of both the Irish Free State and Northern Ireland and achieving the Irish Republic proclaimed in 1916.

Origins
The Irish Volunteers, founded in 1913, staged the Easter Rising, which aimed at ending British rule in Ireland, in 1916. Following the suppression of the Rising, thousands of Volunteers were imprisoned or interned, leading to the break-up of the organisation. It was reorganised in 1917 following the release of first the internees and then the prisoners. At the army convention held in Dublin in October 1917, Éamon de Valera was elected president, Michael Collins Director for Organisation and Cathal Brugha Chairman of the Resident Executive, which in effect made him Chief of Staff.

Following the success of Sinn Féin in the general election of 1918 and the setting up of the First Dáil (the legislature of the Irish Republic), Volunteers commenced military action against the Royal Irish Constabulary (RIC), the paramilitary police force in Ireland, and subsequently against the British Army. It began with the Soloheadbeg Ambush, when members of the Third Tipperary Brigade led by Séumas Robinson, Seán Treacy, Dan Breen and Seán Hogan, seized a quantity of gelignite, killing two RIC constables in the process.

The Dáil leadership worried that the Volunteers would not accept its authority, given that, under their own constitution, they were bound to obey their own executive and no other body. In August 1919, Brugha proposed to the Dáil that the Volunteers be asked to swear allegiance to the Dáil, but one commentator states that another year passed before the movement took an oath of allegiance to the Irish Republic and its government in "August 1920". In sharp contrast, a contemporary in the struggle for Irish independence notes that by late 1919, the term "Irish Republican Army (IRA)" was replacing "Volunteers" in everyday usage. This change is attributed to the Volunteers, having accepted the authority of the Dáil, being referred to as the "army of the Irish Republic", popularly known as the "Irish Republican Army". Already in September 1917, a group of men from counties Clare and Tipperary charged with illegal drilling were claiming to soldiers of the "Irish Republican Army" and refused to recognise the legitimacy of the court, and insisted they should be treated as prisoners of war.

A power struggle continued between Brugha and Collins, both cabinet ministers, over who had the greater influence. Brugha was nominally the superior as Minister for Defence, but Collins's power base came from his position as Director of Organisation of the IRA and from his membership on the Supreme Council of the Irish Republican Brotherhood (IRB). De Valera resented Collins's clear power and influence, which he saw as coming more from the secretive IRB than from his position as a Teachta Dála (TD) and minister in the Aireacht. Brugha and de Valera both urged the IRA to undertake larger, more conventional military actions for the propaganda effect but were ignored by Collins and Mulcahy. Brugha at one stage proposed the assassination of the entire British cabinet. This was also discounted due to its presumed negative effect on British public opinion. Moreover, many members of the Dáil, notably Arthur Griffith, did not approve of IRA violence and would have preferred a campaign of passive resistance to the British rule. The Dáil belatedly accepted responsibility for IRA actions in April 1921, just three months before the end of the Irish War of Independence.

In practice, the IRA was commanded by Collins, with Richard Mulcahy as second in command. These men were able to issue orders and directives to IRA guerrilla units around the country and at times to send arms and organisers to specific areas. However, because of the localised and irregular character of the war, they were only able to exert limited control over local IRA commanders such as Tom Barry, Liam Lynch in Cork and Seán Mac Eoin in Longford.

The IRA claimed a total strength of 70,000, but only about 3,000 were actively engaged in fighting against the Crown. The IRA distrusted those Irishmen who had fought in the British Army during the First World War as potential informers, but there were a number of exceptions such as Emmet Dalton, Tom Barry and Martin Doyle. The IRA divided its members into three classes, namely "unreliable", "reliable" and "active". The "unreliable" members were those who were nominally IRA members but did not do very much for the struggle, "reliable" members played a supporting role in the war while occasionally fighting and the "active" men those who were engaged in full-time fighting. Of the IRA brigades only about one to two-thirds were considered to be "reliable" while those considered "active" were even smaller. A disproportionate number of the "active" IRA men were teachers, medical students, shoemakers and bootmakers; those engaged in building trades like painters, carpenters and bricklayers; draper's assistants and creamery workers. The Canadian historian Peter Hart wrote "...the guerrillas were disproportionately skilled, trained and urban". Farmers and fishermen tended to be underrepresented in the IRA. Those Irishmen engaged in white-collar trades or working as skilled labourers were much more likely to be involved in cultural nationalist groups like the Gaelic League than farmers or fishermen, and thus to have a stronger sense of Irish nationalism. Furthermore, the authority of the Crown tended to be stronger in towns and cities than in the countryside. Thus, those engaged in Irish nationalist activities in urban areas were much more likely to come into conflict with the Crown, leading to a greater chance of radicalisation. Finally, the British tactic of blowing up the homes of IRA members had the effect of discouraging many farmers from joining the struggle as the destruction of the family farm could easily reduce a farmer and his family to destitution. Of the "active" IRA members, three-quarters were in their late teens or early 20s and only 5% of the "active" men were in the age range of 40 or older. The "active" members were overwhelmingly single men with only 4% being married or engaged in a relationship. The life of an "active" IRA man with the stress of living on the run and constantly being in hiding tended to attract single men who could adjust to this lifestyle far more easily than a man in a relationship. Furthermore, the IRA preferred to recruit single men as it was found that singles could devote themselves more wholeheartedly to the struggle.

Women were active in the republican movement, but almost no women fought with the IRA whose "active" members were almost entirely male. The IRA was not a sectarian group and went out of its way to proclaim it was open to all Irishmen, but its membership was largely Catholic with virtually no Protestants serving as "active" IRA men. Hart wrote that in his study of the IRA membership that he found only three Protestants serving as "active" IRA men between 1919 and 1921. Of the 917 IRA men convicted by British courts under the Defence of the Realm Act in 1919, only one was a Protestant. The majority of those serving in the IRA were practising Catholics, but there was a large minority of "pagans" as atheists or non-practising Catholics who were known in Ireland. The majority of the IRA men serving in metropolitan Britain were permanent residents with very few sent over from Ireland. The majority of the IRA men operating in Britain were Irish-born, but there was a substantial minority who were British-born, something that made them especially insistent on asserting their Irish identity.

IRA campaign and organisation
The IRA fought a guerrilla war against the Crown forces in Ireland from 1919 to July 1921. The most intense period of the war was from November 1920 onwards. The IRA campaign can broadly be split into three phases. The first, in 1919, involved the re-organisation of the Irish Volunteers as a guerrilla army and only sporadic attacks. Organisers such as Ernie O'Malley were sent around the country to set up viable guerrilla units. On paper, there were 100,000 or so Volunteers enrolled after the conscription crisis of 1918. However, only about 15,000 of these participated in the guerrilla war. In 1919, Collins, the IRA's Director of Intelligence, organised the "Squad"—an assassination unit based in Dublin that killed police involved in intelligence work (the Irish playwright Brendan Behan's father Stephen Behan was a member of the Squad). Typical of Collins's sardonic sense of humour, the Squad was often referred to as his "Twelve Apostles". In addition, there were some arms raids on RIC barracks. By the end of 1919, four Dublin Metropolitan Police and 11 RIC men had been killed. The RIC abandoned most of their smaller rural barracks in late 1919. Around 400 of these were burned in a co-ordinated IRA operation around the country in April 1920.

The second phase of the IRA campaign, roughly from January to July 1920, involved attacks on the fortified police barracks located in the towns. Between January and June 1920, 16 of these were destroyed and 29 badly damaged. Several events of late 1920 greatly escalated the conflict. Firstly, the British declared martial law in parts of the country—allowing for internment and executions of IRA men. Secondly, they deployed paramilitary forces, the Black and Tans and Auxiliary Division, and more British Army personnel into the country. Thus, the third phase of the war (roughly August 1920 – July 1921) involved the IRA taking on a greatly expanded British force, moving away from attacking well-defended barracks and instead using ambush tactics. To this end the IRA was re-organised into "flying columns"—permanent guerrilla units, usually about 20 strong, although sometimes larger. In rural areas, the flying columns usually had bases in remote mountainous areas.

The most high-profile violence of the war took place in Dublin in November 1920 and is still known as Bloody Sunday. In the early hours of the morning, Collins' "Squad" killed 14 British spies. In reprisal, that afternoon, British forces opened fire on a football crowd at Croke Park, killing 14 civilians. Towards the end of the day, two prominent Republicans and a friend of theirs were arrested and killed by Crown Forces.

While most areas of the country saw some violence in 1919–1921, the brunt of the war was fought in Dublin and the southern province of Munster. In Munster, the IRA carried out a significant number of successful actions against British troops, for instance, the ambushing and killing of 16 of 18 Auxiliaries by Tom Barry's column at Kilmicheal in West Cork in November 1920, or Liam Lynch's men killing 13 British soldiers near Millstreet early in the next year. At the Crossbarry Ambush in March 1921, 100 or so of Barry's men fought a sizeable engagement with a British column of 1,200, escaping from the British encircling manoeuvre. In Dublin, the "Squad" and elements of the IRA Dublin Brigade were amalgamated into the "Active Service Unit", under Oscar Traynor, which tried to carry out at least three attacks on British troops a day. Usually, these consisted of shooting or grenade attacks on British patrols. Outside Dublin and Munster, there were only isolated areas of intense activity. For instance, the County Longford IRA under Seán Mac Eoin carried out a number of well-planned ambushes and successfully defended the village of Ballinalee against Black and Tan reprisals in a three-hour gun battle. In County Mayo, large-scale guerrilla action did not break out until spring 1921, when two British forces were ambushed at Carrowkennedy and Tourmakeady. Elsewhere, fighting was more sporadic and less intense.

In Belfast, the war had a character all of its own. The city had a Protestant and unionist majority and IRA actions were responded to with reprisals against the Catholic population, including killings (such as the McMahon killings) and the burning of many homes – as on Belfast's Bloody Sunday. The IRA in Belfast and the North generally, although involved in protecting the Catholic community from loyalists and state forces, undertook a retaliatory arson campaign against factories and commercial premises. The violence in Belfast alone, which continued until October 1922 (long after the truce in the rest of the country), claimed the lives of between 400 and 500 people.

In April 1921, the IRA was again reorganised, in line with the Dáil's endorsement of its actions, along the lines of a regular army. Divisions were created based on region, with commanders being given responsibility, in theory, for large geographical areas. In practice, this had little effect on the localised nature of the guerrilla warfare.

In May 1921, the IRA in Dublin attacked and burned the Custom House. The action was a serious setback as five members were killed and eighty captured.

By the end of the war in July 1921, the IRA was hard-pressed by the deployment of more British troops into the most active areas and a chronic shortage of arms and ammunition. It has been estimated that the IRA had only about 3,000 rifles (mostly captured from the British) during the war, with a larger number of shotguns and pistols. An ambitious plan to buy arms from Italy in 1921 collapsed when the money did not reach the arms dealers. Towards the end of the war, some Thompson submachine guns were imported from the United States; however 450 of these were intercepted by the American authorities and the remainder only reached Ireland shortly before the Truce.

By June 1921, Collins' assessment was that the IRA was within weeks, possibly even days, of collapse. It had few weapons or ammunition left. Moreover, almost 5,000 IRA men had been imprisoned or interned and over 500 killed. Collins and Mulcahy estimated that the number of effective guerrilla fighters was down to 2,000–3,000. However, in the summer of 1921, the war was abruptly ended.

The British recruited hundreds of World War I veterans into the RIC and sent them to Ireland. Because there was initially a shortage of RIC uniforms, the veterans at first wore a combination of dark green RIC uniforms and khaki British Army uniforms, which inspired the nickname "Black and Tans". The brutality of the Black and Tans is now well-known, although the greatest violence attributed to the Crown's forces was often that of the Auxiliary Division of the Constabulary. One of the strongest critics of the Black and Tans was King George V who in May 1921 told Lady Margery Greenwood that "he hated the idea of the Black and Tans."

The IRA was also involved in the destruction of many stately homes in Munster. The Church of Ireland Gazette recorded numerous instances of Unionists and Loyalists being shot, burnt or forced from their homes during the early 1920s. In County Cork between 1920 and 1923 the IRA shot over 200 civilians of whom over 70 (or 36%) were Protestants: five times the percentage of Protestants in the civilian population. This was due to the historical inclination of Protestants towards loyalty to the United Kingdom. A convention of Irish Protestant Churches in Dublin in May 1922 signed a resolution placing "on record" that "hostility to Protestants by reason of their religion has been almost, if not wholly, unknown in the twenty-six counties in which Protestants are in the minority."

Many historic buildings in Ireland were destroyed during the war, most famously the Custom House in Dublin, which was disastrously attacked on de Valera's insistence, to the horror of the more militarily experienced Collins. As he feared, the destruction proved a pyrrhic victory for the Republic, with so many IRA men killed or captured that the IRA in Dublin suffered a severe blow.

This was also a period of social upheaval in Ireland, with frequent strikes as well as other manifestations of class conflict. In this regard, the IRA acted to a large degree as an agent of social control and stability, driven by the need to preserve cross-class unity in the national struggle, and on occasion being used to break strikes.

Assessments of the effectiveness of the IRA's campaign vary. They were never in a position to engage in conventional warfare. The political, military and financial costs of remaining in Ireland were higher than the British government was prepared to pay and this in a sense forced them into negotiations with the Irish political leaders. According to historian Michael Hopkinson, the guerrilla warfare "was often courageous and effective". Historian David Fitzpatrick observes, "The guerrilla fighters...were vastly outnumbered by the forces of the Crown... The success of the Irish Volunteers in surviving so long is therefore noteworthy."

Truce and treaty
David Lloyd George, the British Prime Minister, at the time, found himself under increasing pressure (both internationally and from within the British Isles) to try to salvage something from the situation. This was a complete reversal on his earlier position. He had consistently referred to the IRA as a "murder gang" up until then. An unexpected olive branch came from King George V, who, in a speech in Belfast called for reconciliation on all sides, changed the mood and enabled the British and Irish Republican governments to agree to a truce. The Truce was agreed on 11 July 1921. On 8 July, de Valera met General Nevil Macready, the British commander in chief in Ireland and agreed terms. The IRA was to retain its arms and the British Army was to remain in barracks for the duration of peace negotiations. Many IRA officers interpreted the truce only as a temporary break in fighting. They continued to recruit and train volunteers, with the result that the IRA had increased its number to over 72,000 men by early 1922. Negotiations on an Anglo-Irish Treaty took place in late 1921 in London. The Irish delegation was led by Arthur Griffith and Michael Collins.

The most contentious areas of the Treaty for the IRA were abolition of the Irish Republic declared in 1919, the status of the Irish Free State as a dominion in the British Commonwealth and the British retention of the so-called Treaty Ports on Ireland's south coast. These issues were the cause of a split in the IRA and ultimately, the Irish Civil War.

Under the Government of Ireland Act 1920, Ireland was partitioned, creating Northern Ireland and Southern Ireland. Under the terms of the Anglo-Irish agreement of 6 December 1921, which ended the war (1919–21), Northern Ireland was given the option of withdrawing from the new state, the Irish Free State, and remaining part of the United Kingdom. The Northern Ireland parliament chose to do that. An Irish Boundary Commission was then set up to review the border.

Irish leaders expected that it would so reduce Northern Ireland's size, by transferring nationalist areas to the Irish Free State, as to make it economically unviable. Partition was not by itself the key breaking point between pro- and anti-Treaty campaigners; both sides expected the Boundary Commission to greatly reduce Northern Ireland. Moreover, Michael Collins was planning a clandestine guerrilla campaign against the Northern state using the IRA. In early 1922, he sent IRA units to the border areas and sent arms to northern units. It was only afterwards, when partition was confirmed, that a united Ireland became the preserve of anti-Treaty Republicans.

IRA and the Anglo-Irish Treaty
The IRA leadership was deeply divided over the decision by the Dáil to ratify the Treaty. Despite the fact that Michael Collins – the de facto leader of the IRA – had negotiated the Treaty, many IRA officers were against it. Of the General Headquarters (GHQ) staff, nine members were in favour of the Treaty while four opposed it. The majority of the IRA rank-and-file were against the Treaty; in January–June 1922, their discontent developed into open defiance of the elected civilian Provisional government of Ireland.

Both sides agreed that the IRA's allegiance was to the (elected) Dáil of the Irish Republic, but the anti-Treaty side argued that the decision of the Dáil to accept the Treaty (and set aside the Irish Republic) meant that the IRA no longer owed that body its allegiance. They called for the IRA to withdraw from the authority of the Dáil and to entrust the IRA Executive with control over the army. On 16 January, the first IRA division – the 2nd Southern Division led by Ernie O'Malley – repudiated the authority of the GHQ. A month later, on 18 February, Liam Forde, O/C of the IRA Mid-Limerick Brigade, issued a proclamation stating that: "We no longer recognise the authority of the present head of the army, and renew our allegiance to the existing Irish Republic". This was the first unit of the IRA to break with the pro-Treaty government.

On 22 March, Rory O'Connor held what was to become an infamous press conference and declared that the IRA would no longer obey the Dáil as (he said) it had violated its Oath to uphold the Irish Republic. He went on to say that "we repudiate the Dáil ... We will set up an Executive which will issue orders to the IRA all over the country." In reply to the question on whether this meant they intended to create a military dictatorship, O'Connor said: "You can take it that way if you like."

On 28 March, the (anti-Treaty) IRA Executive issued statement stating that Minister of Defence (Richard Mulcahy) and the Chief-of-Staff (Eoin O'Duffy) no longer exercised any control over the IRA. In addition, it ordered an end to the recruitment to the new military and police forces of the Provisional Government. Furthermore, it instructed all IRA units to reaffirm their allegiance to the Irish Republic on 2 April. The stage was set for civil war over the Treaty.

Civil War
The pro-treaty IRA soon became the nucleus of the new (regular) Irish National Army created by Collins and Richard Mulcahy. British pressure, and tensions between the pro- and anti-Treaty factions of the IRA, led to a bloody civil war, ending in the defeat of the anti-Treaty faction. On 24 May 1923, Frank Aiken, the (anti-treaty) IRA Chief-of-Staff, called a cease-fire. Many left political activity altogether, but a minority continued to insist that the new Irish Free State, created by the "illegitimate" Treaty, was an illegitimate state. They asserted that their "IRA Army Executive" was the real government of a still-existing Irish Republic. The IRA of the Civil War and subsequent organisations that have used the name claim lineage from that group, which is covered in full at Irish Republican Army (1922–1969).

''For information on later organisations using the name Irish Republican Army, see the table below. For a genealogy of organisations using the name IRA after 1922, see List of organisations known as the Irish Republican Army''.

title: Irish Republican Army (1919–1922)