The Irish War of Independence, sometimes called the Anglo-Irish War, spanned roughly from 1919, when the Irish Volunteers reformed into the Irish Republican Army (IRA) and resumed their armed resistance to British forces in Ireland, to 1921, with the signing of the Anglo-Irish Treaty.

The concentrated Irish struggle against English rule that led to the War of Independence reignited in 1916 with the Easter Rising, in which members of the Irish Republican... Brotherhood, Irish Volunteers, Irish Citizen Army, and Sinn Féin led an insurgence against British forces in Dublin and declared the establishment of an independent Irish republic. After a week of fighting, the British executed fifteen leaders of the rebellion and incarcerated thousands of other participants, spurring a wave of republican nationalist sentiment across Ireland. This was further reinforced by the Conscription Crisis of 1918, in which England attempted to conscript Irishmen into the British Army for service on the Western Front of World War I.

The December 1918 General Election saw mass support for Sinn Féin candidates who, instead of taking their seats in Westminster in London, formed Dáíl Éireann, a new independent government of Ireland, on January 21, 1919. The Irish Volunteers became the army of the new Irish Republic, called the Irish Republican Army (IRA), and waged a guerilla war against the British government forces (primarily the Royal Irish Constabulary, known as the Black and Tans) and British loyalists in Ulster. Republicans also wielded propaganda campaigns, hunger strikes in British prisons, labor strikes, and general protests to rally their cause and gain international sympathy.

In October 1921, the British Prime Minister and the IRA agreed to a ceasefire and began negotiations to end the war. The resulting Anglo-Irish Treaty led to the formation of the Irish Free State in 1922, consisting of 26 counties and a separate six-county Northern Ireland that was to remain under British control. The compromises established by the Treaty divided the Republican cause between those who accepted it and those who would only accept complete independence. This division erupted into the Irish Civil War, which lasted until 1923 and continued to simmer throughout the twentieth century, including a period of violent conflict between Protestant unionists and Roman Catholic nationalists in Northern Ireland known as The Troubles (roughly 1968-1998).

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"Exploring the Irish Wars, 1919-1923," National Museum of Ireland. https://www.museum.ie/en-ie/collections-research/art-and-industry-collections/exploring-the-irish-wars,-1919-1923. Accessed January 9, 2025.

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"Irish War of Independence," Wikipedia, January 9, 2025. https://en.wikipedia.org/wiki/Irish_War_of_Independence.

"Timeline of the Irish War of Independence," Wikipedia, December 31, 2024. https://en.wikipedia.org/wiki/Timeline_of_the_Irish_War_of_Independence.