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.
Republic of Ireland
In the Northern Ireland question, the British and Irish governments started to seek a peaceful resolution to the violent conflict involving many paramilitaries and the British Army in Northern Ireland known as "The Troubles". A peace settlement for Northern Ireland, known as the Good Friday Agreement, was approved in 1998 in referendums north and south of the border. As part of the peace settlement, the territorial claim to Northern Ireland in Articles 2 and 3 of the Constitution of Ireland was removed by referendum. In its white paper on Brexit the United Kingdom government reiterated its commitment to the Good Friday Agreement. With regard to Northern Ireland's status, it said that the UK Government's "clearly-stated preference is to retain Northern Ireland’s current constitutional position: as part of the UK, but with strong links to Ireland".