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 The latter were withdrawn soon afterwards upon the establishment of the Provisional Government, but the former continued to issue revenue stamps until the late 20th century.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.
United Kingdom of Great Britain and Ireland
Growing desire for Irish self-governance led to the Irish War of Independence, which resulted in most of Ireland seceding from the Union and forming the Irish Free State in 1922. Northern Ireland remained part of the Union, and the state was renamed to the current "United Kingdom of Great Britain and Northern Ireland" in 1927. The modern-day United Kingdom is the same country as the one from this period—a direct continuation of what remained after the secession—not an entirely new successor state.