Six months after the Anglo-Irish Treaty ended the recent Irish War of Independence, it was fought between the forces of the new Provisional Government and a section of the Irish Republican Army (IRA) that opposed the Treaty. The Irish Citizen Army also became involved in the Battle, supporting the anti-Treaty IRA in the O'Connell Street area. The fighting began with an assault by Provisional Government forces on the Four Courts building, and ended in a decisive victory for the Provisional Government.