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.
United Ireland
The Northern Ireland Act 1998 supersedes previous similar legislative provisions. The Northern Ireland Constitution Act 1973 also provided that Northern Ireland remained part of the United Kingdom unless a majority voted otherwise in a referendum, while under the Ireland Act 1949 the consent of the Parliament of Northern Ireland was needed for a united Ireland. In 1985, the Anglo-Irish Agreement affirmed that any change in the status of Northern Ireland would only come about with the consent of a majority of the people of Northern Ireland.