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.
The Troubles
Northern Ireland remained a part of the United Kingdom, albeit under a separate system of government whereby it was given its own parliament and devolved government. While this arrangement met the desires of unionists to remain part of the United Kingdom, nationalists largely viewed the partition of Ireland as an illegal and arbitrary division of the island against the will of the majority of its people. They argued that the Northern Ireland state was neither legitimate nor democratic, but created with a deliberately gerrymandered unionist majority. Catholics initially composed about 35% of its population. A total of 557 people, mostly Catholics, were killed in political or sectarian violence from 1920 to 1922 in the six counties that would become Northern Ireland, both during and after the Irish War of Independence. The result was communal strife between Catholics and Protestants, with some historians describing this violence, especially that in Belfast, as a pogrom, although historian Peter Hart argues that the term is not appropriate given the reciprocity of violence in Northern Ireland.