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 Southern Ireland stamps saw little use since that political entity was quickly superseded by the Provisional Government of Ireland and later the Irish Free State (both of which applied overprints on various British and Irish revenue stamps).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.
Republic of Ireland
In the Northern Ireland question, the British and Irish governments started to seek a peaceful resolution to the violent conflict involving many paramilitaries and the British Army in Northern Ireland known as "The Troubles". A peace settlement for Northern Ireland, known as the Good Friday Agreement, was approved in 1998 in referendums north and south of the border. As part of the peace settlement, the territorial claim to Northern Ireland in Articles 2 and 3 of the Constitution of Ireland was removed by referendum. In its white paper on Brexit the United Kingdom government reiterated its commitment to the Good Friday Agreement. With regard to Northern Ireland's status, it said that the UK Government's "clearly-stated preference is to retain Northern Ireland’s current constitutional position: as part of the UK, but with strong links to Ireland".