The campaign for Irish home rule was one of the dominant forces in British politics in the late 19th and early 20th centuries, particularly in that Irish nationalists frequently held the balance of power in the House of Commons. A Home Rule Act was finally passed in 1914 but was suspended until after the First World War; after the Easter Rising of 1916 and Sinn Fein's successes in the general election of 1918, southern Ireland became the Irish Free State in 1921.