Revenue stamps of the United Kingdom
When Ireland was partitioned into Northern Ireland and Southern Ireland in 1921, separate revenue stamps were issued for both entities. Southern Ireland stamps saw little use since that political entity was quickly superseded by the Provisional Government of Ireland and later the Irish Free State (both of which applied overprints on various British and Irish revenue stamps). However, Northern Ireland continued to use separate revenue stamps until the 1980s. Northern Irish revenues include Civil Service, Dog Licence, Excise and National Insurance stamps, among many others.
Irish Republic
The War of Independence ended with the Anglo-Irish Treaty, signed on 6 December 1921 and narrowly approved by Dáil Éireann on 7 January 1922. A Provisional Government was set up under the terms of the treaty, but the Irish Republic nominally remained in existence until 6 December 1922, when 26 of the island's 32 counties became a self-governing British Dominion called the Irish Free State. The island had been partitioned by the Government of Ireland Act 1920, and the six counties of Northern Ireland exercised their right under the Treaty to opt out of the Free State, and remain in the United Kingdom.