Why Ireland Is Partitioned: The Border Between North & South

The border between Northern Ireland (UK) and the Republic of Ireland (sovereign) originates from the Government of Ireland Act 1920 and the Anglo-Irish Treaty 1921.

The Mechanism

1. 1920 Act: Partitioned Ireland into two self-governing entities within the UK:
   • Northern Ireland: 6 NE counties (Antrim, Down, Armagh, Fermanagh, Londonderry, Tyrone) — Protestant/Unionist majority.
   • Southern Ireland: 26 counties — Catholic/Nationalist majority.
2. 1921 Treaty: Ended War of Independence. Southern Ireland became the Irish Free State (Dominion). Northern Ireland opted out (per Treaty Article 12) and rejoined UK.
3. Boundary Commission (1924–25): Supposed to adjust border per Catholic/Protestant majorities. Suppressed; border frozen at 1920 lines.
4. 1937 Constitution: Free State → "Ireland" (Éire), claimed whole island (Articles 2 & 3).
5. 1949: Republic of Ireland Act — left Commonwealth.
6. 1998 Good Friday Agreement: Consent principle — unity only by simultaneous majorities North & South. Articles 2 & 3 amended to aspiration. Cross-border bodies created.

Why the 6 Counties?

Unionists demanded a territory with a secure Protestant majority (65:35 in 1920). Including Donegal, Cavan, Monaghan (Catholic-majority) would have made NI ungovernable. The 6-county unit maximized Unionist control.

Today

• Open border (Common Travel Area + EU Single Market for goods via Windsor Framework).
• Identity: Census 2021: NI — 42% Catholic, 37% Protestant, 17% none/other. First Catholic plurality.
• Polling: United Ireland support ~30–35% in NI; higher in South. Requires concurrent referendums.

The border is a 20th-century political artifact — not ancient, not natural, but deeply consequential.