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 Southern Ireland stamps saw little use since that political entity was quickly superseded by the Provisional Government of Ireland and later the Irish Free State (both of which applied overprints on various British and Irish revenue stamps).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.
Partition of Ireland
The Government of Ireland Act 1920, which came into effect on 3 May 1921, provided for separate self-governing parliaments for Northern Ireland (the six northeastern counties) and Southern Ireland (the rest of the island), thus partitioning Ireland. While the parliament and governmental institutions for Northern Ireland were soon established, the election in the 26 counties returned an overwhelming majority of members giving their allegiance to Dáil Éireann and supporting the republican effort in the Irish War of Independence, thus rendering "Southern Ireland" dead in the water.