Partition of Ireland
The partition of Ireland () divided the island of Ireland into two distinct jurisdictions, Northern Ireland and Southern Ireland. It took place on 3 May 1921 under the Government of Ireland Act 1920. Today the former is still known as Northern Ireland and forms part of the United Kingdom, while the latter is now a sovereign state also named Ireland and sometimes called the Republic of Ireland.
History of the United Kingdom
In 1922, Catholic Ireland seceded to become the Irish Free State; a day later, Northern Ireland seceded from the Free State and returned to the United Kingdom. In 1927 the United Kingdom changed its formal title to the "United Kingdom of Great Britain and Northern Ireland," usually shortened to "Britain" and (after 1945) to the "United Kingdom" or "UK".