The Irish War of Independence (Irish: Cogadh na Saoirse), also known as the Anglo–Irish War, began in January 1919 as a guerrilla war waged by the Irish Republican Army (IRA) against the British Government. Ireland was formally a part of the United Kingdom as a result of the passing of the Acts of Union in 1800. In the late-nineteenth century, the Irish Parliamentary Party, led by Charles Stewart Parnell (1846–1891), advocated home rule for Ireland through cooperation with the Liberal Party in the English Parliament, but it was unsuccessful until the Third Home Rule Bill of 1912. This bill provoked Unionists in the north of Ireland to form the Ulster Volunteers, who feared a predominantly Catholic Irish Parliament in Dublin. In response, Nationalists formed the Irish Volunteers. The Third Home Rule Bill never took effect because of the outbreak of World War I; Irish troops fought with England in the war with the promise that home rule would be granted at the conflict’s end.