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.
Northern Ireland
As a consequence of the worsening security situation, autonomous regional government for Northern Ireland was suspended in 1972. Alongside the violence, there was a political deadlock between the major political parties in Northern Ireland, including those who condemned violence, over the future status of Northern Ireland and the form of government there should be within Northern Ireland. In 1973, Northern Ireland held a referendum to determine if it should remain in the United Kingdom, or be part of a united Ireland. The vote went heavily in favour (98.9%) of maintaining the status quo. Approximately 57.5% of the total electorate voted in support, but only 1% of Catholics voted following a boycott organised by the Social Democratic and Labour Party (SDLP).