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.
Northern Ireland Constitution Act 1973
When the Republic of Ireland ceased to be a member of the British Commonwealth, Westminster had responded with the Ireland Act 1949. Amongst its other provisions, the Act had guaranteed that Northern Ireland would not cease to remain a part of the United Kingdom "without the consent of the Parliament of Northern Ireland" (s. 1(2)); this declaration had proven to be controversial both with the Irish government and with Northern Ireland's nationalist community.