The
Irish Republican Army (
IRA) () was an
Irish republican revolutionary military organisation. The ancestor to many groups also known as the
Irish Republican Army, it was descended from the
Irish Volunteers, an organisation established on 25 November 1913 that staged the
Easter Rising in April 1916. In 1919, the
Irish Republic that had been proclaimed during the Easter Rising was formally established by an elected assembly (
Dáil Éireann), and the Irish Volunteers were recognised by Dáil Éireann as its legitimate army. Thereafter, the IRA waged a
guerrilla campaign against British rule in Ireland in the 1919–21
Irish War of Independence.