Ninety One Years ago today, the peace talks between the Irish Republicans and the United Kingdom led to the negotiation of the Anglo-Irish Treaty (6 December 1921), which was then ratified in triplicate: by Dáil Éireann on 7 January 1922 (so giving it legal legitimacy under the governmental system of the Irish Republic), by the House of Commons of Southern Ireland in January, 1922 (so giving it constitutional legitimacy according to British theory of who was the legal government in Ireland), and by both Houses of the British parliament.
The treaty allowed Northern Ireland, which had been created by the Government of Ireland Act, 1920, to opt out of the Free State if it wished, which it duly did on 8 December 1921 under the procedures laid down. As agreed, an Irish Boundary Commission was then created to decide on the precise location of the border of the Free State and Northern Ireland.
The republican negotiators understood that the Commission would redraw the border according to local nationalist or unionist majorities. Since the 1920 local elections in Ireland had resulted in outright nationalist majorities in County Fermanagh, County Tyrone, the City of Derry and in many District Electoral Divisions of County Armagh and County Londonderry (all north and west of the "interim" border), this might well have left Northern Ireland unviable. However, the Commission chose to leave the border unchanged; as a trade-off, the money owed to Britain by the Free State under the Treaty was not demanded.