The Irish War of Independence, also called the Anglo-Irish War, took place from 1919 to 1921. Fighting took place between the Irish Republican Army (IRA) and British forces, which included the British Army, the Royal Irish Constabulary (RIC), and paramilitary forces from the Auxiliaries and Ulster Special Constabulary (USC).

Although Irish rebellions had occurred several times throughout England’s occupation of Ireland (including early uprisings like O’Doherty’s Rebellion in 1607), the successful rebellion and war for independence took root nearly three years prior to the start of the war. The Easter Rising of 1916, launched by Irish republicans, generated increased support for Irish independence and led to a landslide election victory for Sinn Féin, the Irish republican party, in December 1918. The Irish War of Independence began when Sinn Féin formed a breakaway government called Dáil Éireann and declared Irish independence. IRA volunteers acted on their own initiative that day, killing two RIC officers in an ambush.

The war began gradually, and the IRA forces utilized guerilla warfare. For much of 1919, the IRA mostly captured weapons and freed republican prisoners; meanwhile, the Dáil built their state government, which was outlawed by the British government. The IRA increased their activities, ambushing RIC and British army patrols and attacking barracks.