why did northern ireland separate from the rest of ireland
Partition of Ireland The Act of 1920 was intended to create two self-governing territories within Ireland, with both remaining within the United Kingdom. It also contained provisions for co-operation between the two territories and for the eventual reunification of Ireland. However, in 1922, following the War of Independence and the Anglo-Irish Treaty, the southern part became the Irish Free State, while Northern Ireland exercised its option to remain in the United Kingdom.
United Kingdom of Great Britain and Ireland The growing desire for Irish self-governance led to the Irish War of Independence after the First World War, which resulted in most of Ireland seceding from the Union and forming the Irish Free State in 1922. Northern Ireland remained part of the United Kingdom, and the state was consequently renamed the "United Kingdom of Great Britain and Northern Ireland".