Irish Republican Army

Flying Column No. 2 of the 3rd Tipperary Brigade of the Old IRA, photographed during the early 1920s. All organisations calling themselves "Irish Republican Army" claim legitimate descent (sometimes compared to apostolic succession) from this IRA of 1919–1922. The Irish Republican Army (IRA) is a name used by various militant organisations in Ireland throughout the 20th and 21st centuries. Organisations by this name have been dominantly Catholic and dedicated to anti-imperialism through Irish republicanism, the belief that all of Ireland should be an independent republic free from British colonial rule.

The original Irish Republican Army (1919–1922), often now referred to as the "old IRA", was raised in 1919 from members of the Irish Volunteers and the Irish Citizen Army later reinforced by Irishmen formerly in the British Army in World War I, who returned to Ireland to fight against Britain in the Irish War of Independence. In Irish law, this IRA was the army of the revolutionary Irish Republic as declared by its parliament, Dáil Éireann, in 1919.