The Irish Civil War began on June 28, 1922, and was a conflict between Irish Nationalists and Irish Republicans over the Anglo-Irish Treaty. This treaty had ended the Irish War of Independence (1919-1921) and created an Irish Free State from which Britain would withdraw its police and army. It also gave the six northern counties the option of withdrawing from Ireland and return to the United Kingdom--a choice they accepted almost immediately.
After intense fighting between the Free State government and the Anti-Treaty IRA, the civil war was brought to an end on May 24, 1923, when the head of state, Eamon de Valera, called a ceasefire and ordered all fighters to return home. Fortunately, this was accepted by both sides as the war's formal conclusion and no official surrender nor peace negotiations ever took place.