Ireland–United Kingdom border

Six counties

From the first Home Rule bill of 1886, Protestant unionists, most of them in the north, resisted being ruled by a Catholic-majority parliament in Dublin. When the third bill passed in 1914, Ulster had armed volunteers and civil war seemed close, until the war in Europe put Home Rule on hold.^[4] After the Easter Rising of 1916 and Sinn Féin’s victory in 1918, the Irish War of Independence began in 1919.^[4]

The Government of Ireland Act of 1920 created two home-rule units: six of Ulster’s nine counties, soon called Northern Ireland, and the other 26 counties. The north accepted it and its parliament met in June 1921; the south rejected it. The Anglo-Irish Treaty of December 1921 made the south the Irish Free State, a dominion, and let Northern Ireland opt out, which it did.^[4]

A boundary left alone

The treaty set up a boundary commission to review the line. Its report in 1925 proposed only small swaps, parts of Fermanagh, Tyrone and Armagh to the Free State and part of Donegal to the north, but both governments opposed them and the report was never issued. An agreement of 3 December 1925 left the border on the outer edges of Antrim, Armagh, Down, Fermanagh, Londonderry and Tyrone.^[4]

No line was ever drawn through the two sea loughs at its ends. The Free State claimed all of Lough Foyle, up to the shore of County Derry; in the 1920s the rival claims led to court fights and armed confrontations over the salmon fishery, until both governments set up a joint fisheries authority in 1950.^[3]

The Troubles and the agreement

From about 1968 to 1998 Northern Ireland was torn by conflict between mostly Protestant unionists, who wanted to stay in the United Kingdom, and mostly Catholic nationalists, who wanted to join the Irish state. Some 3,600 people were killed and more than 30,000 wounded.^[5]

The Good Friday Agreement, signed in Belfast on 10 April 1998, set up a power-sharing Northern Ireland Assembly, cross-border cooperation between Ireland and Northern Ireland, and consultation between London and Dublin. It was approved by 94% of voters in the south and 71% in the north. When it took effect on 2 December 1999, Ireland dropped its constitutional claim to the whole island.^[6]

“the first all-Ireland vote since 1918”^[6]

Brexit

In the 2016 referendum Northern Ireland voted 56% to remain in the EU, but the UK as a whole voted to leave, and the border became the hardest problem of the negotiations.^[1] Both sides feared that posts on the border would become paramilitary targets and endanger the peace.^[2]

Rather than checks at some 270 crossings, the UK and the EU agreed the Protocol on Ireland/Northern Ireland, in force from 1 January 2021: Northern Ireland follows EU rules for goods, so goods cross the land border freely, and the checks happen instead on goods arriving from Great Britain. The Windsor Framework of 2023 eased those checks with a “green lane” for goods staying in Northern Ireland. The land border stays open, with no checks.^[1]