The War of Independence

1917 - 1923 — After the 1916 executions, support for independence surged. Sinn Féin's 1918 landslide led to the War of Independence, the Anglo-Irish Treaty, partition and Civil War.

The executions after the 1916 Rising transformed Irish public opinion: hostility to the rebels turned to sympathy, and then to a surge of support for full independence. In the general election of December 1918, the pro-independence party Sinn Féin won a landslide across most of Ireland. Rather than take their seats at Westminster, its elected members set up their own parliament in Dublin, Dáil Éireann, and declared an independent Irish Republic in January 1919.

That same period saw the outbreak of the War of Independence (1919–1921), a guerrilla conflict fought by the Irish Republican Army (IRA) against British forces and the feared auxiliary police known as the "Black and Tans". Figures such as Michael Collins directed a ruthless campaign of ambushes, raids and intelligence work, met by harsh reprisals.

A truce in July 1921 led to the Anglo-Irish Treaty of December 1921. The Treaty created the Irish Free State, a self-governing dominion, but partitioned the island — leaving six counties in the north as Northern Ireland within the United Kingdom. Bitter disagreement over the Treaty split the independence movement and led to the Irish Civil War (1922–1923) between pro- and anti-Treaty forces, a painful conflict whose divisions would shape Irish politics for generations.