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 Declaration of Independence
This was based on the 'apostolic succession' of revolts against the English and later, British Administrations, placing the last fully free Ireland in the Gaelic world of about the 1160s, before the Norman invasion of Ireland of 1168–71. The declaration saw the wars and revolts of 1594–1603, 1641–50, 1689–91, 1798, 1803, 1848, 1867 and 1916 as a continuing attempt at regaining Irish self-government, with or without links to the crown.