Republic of Ireland–United Kingdom border
Originally intended as an internal boundary within the United Kingdom of Great Britain and Ireland, the border was created in 1921 under the United Kingdom Parliament's Government of Ireland Act 1920. Prior to this, a separatist Irish parliament had been established in Dublin, which did not recognise the Government of Ireland Act, and was actively engaged in the Irish War of Independence. The Act was intended to deliver Home Rule in Ireland, with separate parliaments for Southern Ireland (which included three of the nine counties of Ulster) and Northern Ireland. Six of the thirty-two counties of Ireland were assigned to Northern Ireland, and the rest of Ireland comprising 26 counties to Southern Ireland.
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.