Guerrilla War Ends in a Treaty and a Partitioned Island
Two and a half years of ambush and reprisal end in a truce, a treaty, and a border that splits six counties from the rest
Quick facts
- War began
- 21 January 1919, Soloheadbeg, Co. Tipperary
- Truce
- July 1921
- Anglo-Irish Treaty signed
- 6 December 1921
- Dail ratification margin
- 7 votes
What happened
The Irish War of Independence broke out on 21 January 1919, the same day the breakaway Irish parliament, Dail Eireann, first assembled, when two Royal Irish Constabulary officers were killed at Soloheadbeg, County Tipperary. Heavily outnumbered and short of arms, the Irish Republican Army fought a guerrilla campaign of ambushes and assassinations against police and crown forces, while Britain reinforced the police with recruits nicknamed the Black and Tans for their mismatched uniforms. A truce was agreed in July 1921, and the Anglo-Irish Treaty followed on 6 December 1921, ending the war and creating the Irish Free State as a self-governing dominion. Under the terms already set by the 1920 Government of Ireland Act, the six northeastern counties with a Protestant majority formed Northern Ireland and immediately opted to remain inside the United Kingdom rather than join the new Free State, which the Dail ratified by a narrow margin of seven votes. An Irish Boundary Commission later confirmed the border largely as originally drawn.
Why it matters
The Treaty ended direct British rule over most of Ireland after roughly 750 years, but the partition it confirmed and the narrow Dail vote that ratified it split Irish nationalism into pro- and anti-Treaty factions and triggered the Irish Civil War within months, while the border itself became the central, unresolved fault line of 20th-century Irish and Northern Irish politics.
How we know
The War of Independence, the 1921 truce, the Anglo-Irish Treaty, and the Government of Ireland Act 1920 are documented in British and Irish government records of the period, held respectively by the UK National Archives and Irish state archives, including the Dail's own ratification vote record.
Sources
- National Army Museum (UK). Irish War of Independence · Reputable sourcenam.ac.uk · The domain "nam.ac.uk" is on our Reputable source registry. · Link is live and its text matches the event's key terms (Jul 2026)
- The National Archives (UK). Irish Partition · Reputable sourcenationalarchives.gov.uk · The domain "nationalarchives.gov.uk" is on our Reputable source registry. · Link is live and its text matches the event's key terms (Jul 2026)
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Related timelines
- The British Empire → · The Irish Free State's 1922 status as a self-governing dominion mirrored the constitutional position of Canada and other dominions inside the British Empire; see the British Empire timeline for how that dominion structure worked elsewhere.