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.
Irish issue in British politics
Home Rule was passed in 1914, but suspended in operation during the First World War. The issue was finally resolved in 1921 by partitioning Ireland into the quasi-autonomous (Catholic-dominated) Irish Free State in the southwestern four-fifths of the island, and (Prebyterian dominated) Northern Ireland in the remaining fifth, which remained part of the United Kingdom. The next round of troubles emerged in the 1960s, when the Catholics living in Northern Ireland could no longer tolerate the discriminatory policies long imposed on them by the (devolved) government of Northern Ireland. The Troubles 30 years of near civil war that at times had significant impact on British politics finally ended with the Good Friday Agreement of 1998, a power-sharing agreement between the parties in Northern Ireland and a international Treaty between Ireland and the United Kingdom, as co-guarantors.