The Northern Ireland border

The Northern Ireland border came into existence on 3 May 1921, enacted as part of the Government of Ireland Act 1920. This established the Parliament of Northern Ireland (1921-72), whose territorial extent was defined by reference to the six counties of Ulster.

Originally intended as an administrative boundary between two devolved parts of the United Kingdom, by the end of 1922 it marked the border between the UK and the new “Irish Free State”. It took economic form on 1 April 1923, when a customs frontier was erected. Later, the recommendations of a Boundary Commission were rejected and the border was confirmed in December 1925.

The Northern Ireland border reflected traditional county boundaries which pre-dated the events of the early 1920s. “Its shape and location” judged the historian Margaret O’Callaghan, “reflected the inheritance of the past and the balance of social and political forces on and between both islands.”

As the only part of the UK with a land frontier, the Northern Ireland border challenged politicians and administrators since its inception, not least in security terms. In 1956 and again in 1970, the boundary was securitised as a result of paramilitary activity. For the border was also contested. As the historian J. C. Beckett observed in 1952, a border between the “two Irelands” resided not only on maps, “but in the minds of men”.

This paper explores the origins of the Northern Ireland border and then charts its development – economically, geographically and politically – over the century which followed its creation.