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.
Ireland
Northern Ireland resulted from the division of the United Kingdom by the Government of Ireland Act 1920, and until 1972 was a self-governing jurisdiction within the United Kingdom with its own parliament and prime minister. Northern Ireland, as part of the United Kingdom, was not neutral during the Second World War and Belfast suffered four bombing raids in 1941. Conscription was not extended to Northern Ireland and roughly an equal number volunteered from Northern Ireland as volunteered from the south.