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.
Unionism in Ireland
In 1922, twenty-six counties of Ireland gained autonomy from the U.K. as the Irish Free State; in 1949, the State was declared to be a Republic and the last vestiges of royal power were abolished. The Republic of Ireland left the Commonwealth of Nations. The remaining six counties of the island of Ireland constituted the territory of Northern Ireland. In 1927, the realm, consisting of combined territories of Northern Ireland and Great Britain, was renamed the "United Kingdom of Great Britain and Northern Ireland". Today, unionism is almost exclusively an issue for Northern Ireland. It is concerned with the governance of and relationship between Northern Ireland and Great Britain.