Revenue stamps of Northern Ireland
Upon the partition of Ireland in 1921, separate revenue stamps began to be issued for both Northern Ireland and Southern Ireland. The latter were withdrawn soon afterwards upon the establishment of the Provisional Government, but the former continued to issue revenue stamps until the late 20th century. The need for separate issues for Northern Ireland came about since taxes raised there were meant to remain in the country. Most Northern Irish revenue stamps were British key types with appropriate inscriptions, but there were a number of different issues as well.
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.