Irish Civil War

Between June 1922 and May 1923, Irish nationalists who had fought Britain side by side turned their guns on one another. The quarrel was over the Anglo-Irish Treaty, which created the Irish Free State as a self-governing dominion of the British Empire rather than the fully independent republic many had fought for. The government side won, but the split shaped Irish politics for generations.

The treaty ended the Irish War of Independence of 1919–1921. It gave southern Ireland its own government, army and police, but kept the British monarch as head of state, required members of parliament to swear an oath of allegiance, let Northern Ireland stay in the United Kingdom and left several ports in Royal Navy hands. Michael Collins defended it as "the freedom to achieve freedom". Éamon de Valera and many republicans saw it as abandoning the republic proclaimed in the Easter Rising of 1916.

The Dáil approved the treaty by 64 votes to 57 on 7 January 1922. De Valera stepped down as president, and much of the IRA rejected parliament's authority. In April 1922 about 200 anti-treaty fighters seized the Four Courts in Dublin. In the general election of 16 June, pro-treaty candidates and other parties that broadly accepted the settlement won a clear majority.

After the killing of Field Marshal Henry Wilson in London on 22 June, the British government pressed Collins to act. On 28 June the new National Army began shelling the Four Courts with field guns lent by Britain. The garrison surrendered on 30 June; a huge explosion destroyed the Public Record Office and centuries of documents, and historians still argue over whether it was deliberate. Street fighting in the city lasted until 5 July and killed the republican leader Cathal Brugha.

The anti-treaty forces held much of the south, which they called the Munster Republic, and at first may have had around 12,000 men to the government's 8,000. But they lacked artillery, a clear strategy and effective command. British supplies let the National Army grow quickly, to 55,000 soldiers by the war's end. Using columns overland and landings from the sea, it took Limerick and Waterford on 20 July and Cork on 10 August 1922.

The republicans, led by Liam Lynch, switched to ambushes, sabotage of roads and railways, and the burning of country houses. Arthur Griffith died of a brain haemorrhage in August, and ten days later Collins was killed in an ambush at Béal na Bláth in County Cork. Under W. T. Cosgrave the government gave military courts the power to impose death sentences. Official executions began on 17 November 1922 and eventually numbered 81, among them the writer Erskine Childers. After the republicans shot the deputy Seán Hales in December, four captured leaders were executed the next day. In Kerry, troops killed prisoners without trial, most notoriously at Ballyseedy, where eight men died tied to a mine.

By early 1923 the guerrilla campaign was failing, and the Catholic bishops had condemned it. Lynch was killed on 10 April. His successor, Frank Aiken, suspended operations and on 24 May ordered the volunteers to hide their weapons rather than surrender them. No peace treaty was ever signed, and thousands of republicans remained interned for months.

A 2023 research project at University College Cork counted 637 pro-treaty dead and 426 anti-treaty IRA dead, and put total deaths in the Free State at about 1,426; other estimates differ. The war cost tens of millions of pounds and helped settle the partition of the island. Its two sides became Ireland's two main parties: Fine Gael from the pro-treaty side and Fianna Fáil, founded by de Valera in 1926. The state later dismantled the treaty's terms step by step and declared itself a republic in 1948. The modern country is covered on our Ireland page.

Our 1920 map shows Ireland still inside the United Kingdom, and the 1930 map shows the island after the creation of the Free State.