The Troubles
The Government of Ireland Act 1920 partitioned the island of Ireland into two separate jurisdictions, Southern Ireland and Northern Ireland, both devolved regions of the United Kingdom. This partition of Ireland was confirmed when the Parliament of Northern Ireland exercised its right in December 1922 under the Anglo-Irish Treaty of 1921 to ""opt out"" of the newly established Irish Free State. A part of the treaty signed in 1922 mandated that a boundary commission would sit to decide where the frontier of the northern state would be in relation to its southern neighbour. After the Irish Civil War of 1922–1923, this part of the treaty was given less priority by the new Dublin government led by W. T. Cosgrave, and was quietly dropped. As counties Fermanagh and Tyrone and border areas of Londonderry, Armagh, and Down were mainly nationalist, the Irish Boundary Commission could reduce Northern Ireland to four counties or less.
Partition of Ireland
The treaty "went through the motions of including Northern Ireland within the Irish Free State while offering it the provision to opt out". It was certain that Northern Ireland would exercise its opt out. The Prime Minister of Northern Ireland, Sir James Craig, speaking in the House of Commons of Northern Ireland in October 1922, said that "when the 6th of December is passed the month begins in which we will have to make the choice either to vote out or remain within the Free State." He said it was important that that choice be made as soon as possible after 6 December 1922 "in order that it may not go forth to the world that we had the slightest hesitation." On the following day, 7 December 1922, the Parliament resolved to make the following address to the King so as to opt out of the Irish Free State: