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.
1973 Northern Ireland border poll
The Northern Ireland border poll was a referendum held in Northern Ireland on 8 March 1973 on whether Northern Ireland should remain part of the United Kingdom or join with the Republic of Ireland to form a united Ireland. It was the first time that a major referendum had been held in any region of the United Kingdom. The referendum was boycotted by nationalists and resulted in a conclusive victory for remaining in the UK. On a voter turnout of 58.7 percent, 98.9 percent voted to remain in the UK.