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 Southern Ireland stamps saw little use since that political entity was quickly superseded by the Provisional Government of Ireland and later the Irish Free State (both of which applied overprints on various British and Irish revenue stamps).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.
Ulster
Partition of Ireland, first mooted in 1912, was introduced with the enactment of the Government of Ireland Act 1920, which gave a form of "Home rule" self-government to two areas, Southern Ireland, with its capital at Dublin, and "Northern Ireland", consisting of six of Ulster's central and eastern counties, both within a continuing United Kingdom of Great Britain and Ireland. Dissatisfaction with this led to the Irish War of Independence, which formally ceased on 11 July 1921. Low-level violence, however, continued in Ulster, causing Michael Collins in the south to order a boycott of Northern products in protest at attacks on the Nationalist community there. The Partition was effectively confirmed by the Anglo-Irish Treaty of 6 December 1921. One of the primary stipulations of the treaty was the transformation of Ireland into a self-governing British dominion called the Irish Free State (which later became the sovereign Republic of Ireland), but with the option of a continuation of the home rule institution of Northern Ireland, still within the United Kingdom, if the Northern Ireland Parliament (already in existence) chose to opt out of the Irish Free State. All parties knew that this was certain to be the choice of the Ulster Unionists who had a majority in the parliament, and immediately on the creation of the Free State they resolved to leave it.