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.
Counties of Northern Ireland
The English administration in Ireland in the years following the Anglo-Norman invasion of Ireland created counties as the major subdivisions of an Irish province. This process lasted a period from the 13th to 17th centuries, however the number and shape of the counties that would form the future Northern Ireland would not be defined until the Flight of the Earls allowed the shiring of Ulster from 1604.