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 people
After the Irish War of Independence (1919–1921) the Anglo-Irish Treaty was signed which led to the formation of the semi-independent Irish Free State (now the independent Republic of Ireland) which consisted of 26 counties in the south and Donegal in the North-West. The remaining six counties in the northeast remained in the United Kingdom as Northern Ireland. It is predominately religion, historical, and political differences that divide the two communities of (nationalism and unionism). Four polls taken between 1989 and 1994 revealed that when asked to state their national identity, over 79% of Northern Irish Protestants replied "British" or "Ulster" with 3% or less replying "Irish", while over 60% of Northern Irish Catholics replied "Irish" with 13% or less replying "British" or "Ulster". A survey in 1999 showed that 72% of Northern Irish Protestants considered themselves "British" and 2% "Irish", with 68% of Northern Irish Catholics considering themselves "Irish" and 9% "British". The survey also revealed that 78% of Protestants and 48% of all respondents felt "Strongly British", while 77% of Catholics and 35% of all respondents felt "Strongly Irish". 51% of Protestants and 33% of all respondents felt "Not at all Irish", while 62% of Catholics and 28% of all respondents felt "Not at all British".