Partition of Ireland
Beginning on 21 January 1919 with the Soloheadbeg ambush, through the Irish War of Independence, Irish republicans attempted to bring about the secession of Ireland from the United Kingdom of Great Britain and Ireland. Meanwhile, Irish unionistsmost of whom lived in the northeast of the islandwere just as determined to maintain the Union. The British Government, committed to implementing Home Rule, set up a cabinet committee under the chairmanship of southern unionist Walter Long. The Long Committee recommended the establishment of two devolved administrations, dividing the island into two territories: Northern Ireland and Southern Ireland. This was implemented as the Government of Ireland Act 1920. The act entered into force as a "" on 3 May 1921 and provided that Northern Ireland would consist of the six northeastern counties, while the remainder of the island would form Southern Ireland. It was intended that each jurisdiction would be granted home rule but remain within the United Kingdom. The government of Southern Ireland never functioned: the war for independence continued until the two sides agreed a truce in July 1921, ending with the Anglo-Irish Treaty on 6 December 1921.
Ulster
Partition of Ireland, first mooted in 1912, was introduced with the enactment of the Government of Ireland Act 1920, which gave a form of "Home rule" self-government to two areas, Southern Ireland, with its capital at Dublin, and "Northern Ireland", consisting of six of Ulster's central and eastern counties, both within a continuing United Kingdom of Great Britain and Ireland. Dissatisfaction with this led to the Irish War of Independence, which formally ceased on 11 July 1921. Low-level violence, however, continued in Ulster, causing Michael Collins in the south to order a boycott of Northern products in protest at attacks on the Nationalist community there. The Partition was effectively confirmed by the Anglo-Irish Treaty of 6 December 1921. One of the primary stipulations of the treaty was the transformation of Ireland into a self-governing British dominion called the Irish Free State (which later became the sovereign Republic of Ireland), but with the option of a continuation of the home rule institution of Northern Ireland, still within the United Kingdom, if the Northern Ireland Parliament (already in existence) chose to opt out of the Irish Free State. All parties knew that this was certain to be the choice of the Ulster Unionists who had a majority in the parliament, and immediately on the creation of the Free State they resolved to leave it.