One of the more entertaining paradoxes in Irish history is that the northeast of Ireland, which had fought so strenuously against Home Rule for half a century, was the only part of the country to get it. On 23 December 1920 the British parliament passed the Government of Ireland Act, which partitioned the six counties from the rest of the island and established a Home Rule parliament in Belfast. Elections were held in May 1921, and the King opened the first session of the Northern Ireland parliament in Belfast on 22 June 1921. Over the next six months, powers were gradually transferred to a new government controlled by the Unionist Party. Its leader, and the Prime Minister of Northern Ireland until his death in 1940, was Sir James Craig. The son of a millionaire whiskey distiller, and a man with deep Ulster roots, Craig had been a chief organiser of the unionist campaign in 1913 and 1914, before taking up junior positions within the London government during the First World War. He was an able administrator, a skilful politician, and more moderate than many of his partisan loyalist colleagues, but he possessed a strong antipathy towards Irish republicanism and an unyielding determination to protect the interests of the unionist community in the north. His objective during 1921 and 1922 was to create a strong, independent ‘statelet’ that would be insulated from the revolutionary events in southern Ireland and policy changes in London.

The birth of Northern Ireland was a difficult one. The emerging Sinn Féin government in the south refused to accept this settlement of the Irish problem. It waged a continuous propaganda and diplomatic offensive, seeking to undermine the unionist administration and to compel the British government to undo partition. The constitutional future of the six counties was a major sticking point in the Anglo-Irish negotiations during the second half of 1921. An overall settlement was only reached by postponing a resolution of the issue: the delegates agreed to form a Boundary Commission after ratification of the treaty, which would redraw the border.