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 Southern Ireland stamps saw little use since that political entity was quickly superseded by the Provisional Government of Ireland and later the Irish Free State (both of which applied overprints on various British and Irish revenue stamps).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.
Ireland–United States relations
The Irish War of Independence ultimately ended with the Anglo-Irish Treaty, which confirmed the partition of Ireland into the Irish Free State and Northern Ireland, the latter of which opted to remain a part of the United Kingdom. The Irish Free State quickly fell into the Irish Civil War between Pro-Treaty Forces who supported independence via partition and Anti-Treaty Forces who opposed partition and wanted independence for the entire island of Ireland. Pro-Treaty Forces won the Irish Civil War in 1923, and the following year the United States recognized the Irish Free State and established diplomatic relations with it. The Irish Free State was succeeded by the new state of Ireland in 1937, and formally declared itself a republic in 1949.