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.
Irish border question
In 1922, the Irish Free State repatriated its national legislature from London, setting the stage for full national independence, while Northern Ireland remained under the governance of the United Kingdom. Consequently the dividing line between these two parts of the island became an international border. Trade in goods and services across this frontier became subject to differing tax and tariff arrangements and an infrastructure of Customs posts was put in place at designated crossing areas. All traffic was subject to inspection by the jurisdiction it was entering. This could entail full vehicle searches with consequent delay and inconvenience. However, passport checks were not applied because the Republic of Ireland and Northern Ireland were part of the Common Travel Area.