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.
Falls Curfew
The Northern Ireland riots of August 1969 marked the beginning of the Troubles. In Belfast, Catholic Irish nationalists clashed with Protestant Ulster loyalists and the mainly-Protestant Royal Ulster Constabulary (RUC), Northern Ireland’s police force. Hundreds of Catholic homes and businesses were burnt out and more than 1,000 families, mostly Catholics, were forced to flee. The rioting ended with Operation Banner, the deployment of British troops. In December 1969, the IRA split into the 'Official' IRA and 'Provisional' IRA, with the 'Provisionals' promising to defend Catholic areas.