Anglo-Irish War

Conflict in Ireland 1919–21, between the Irish Republican Army (IRA), the paramilitary wing of Sinn Fein, and British government forces, reinforced by the ex-service Auxiliaries and Black and Tans. Its outbreak is usually dated to the IRA's killing of two policemen in Soloheadbeg, County Tipperary, on 21 January 1919. Following a war of guerrilla tactics, ambushes, assassinations, and reprisals, a truce negotiated in July 1921 led to the Anglo-Irish Treaty, which established the Irish Free State. Over 550 soldiers and police and more than 750 volunteers and civilians died during the conflict.

Despite the Soloheadbeg incident, which coincided with the day of the first meeting of the Dáil, the illegal republican parliament in Dublin, IRA attacks against the Royal Irish Constabulary (RIC) and other targets had begun in 1918 against the wishes of Sinn Fein, the political wing of the republican movement. The IRA was nominally controlled by the Dáil minister for defence Cathal Brugha (1874–1922) and IRA headquarters under Michael Collins and Chief of Staff Richard Mulcahy (1886–1971), but little effective control was exercised over local IRA units. Collins's network of spies and assassins effectively disrupted British intelligence in Dublin. The fighting was unevenly distributed and concentrated in central Munster and the border regions of Ulster. IRA volunteers were predominantly drawn from the lower middle-class youths of rural and small-town Ireland.

The conflict escalated in 1920 when the RIC was strengthened with two forces of ex-servicemen known as the Auxiliaries and Black and Tans, which both earned unsavoury reputations. The harsh tactics adopted by government forces and condoned in London, including murder, looting, and arson, undermined the credibility of British rule in Ireland. By the spring of 1920 British forces had withdrawn from hundreds of garrisons in rural Ireland while flying columns, full-time mobile units of ‘on the run’ IRA personnel, engaged in guerrilla tactics. When both sides had fought to near-exhaustion with no clear victor in sight, a truce was called in July 1921 to allow peace talks to begin.