Republic of Ireland–United Kingdom border
Originally intended as an internal boundary within the United Kingdom of Great Britain and Ireland, the border was created in 1921 under the United Kingdom Parliament's Government of Ireland Act 1920. Prior to this, a separatist Irish parliament had been established in Dublin, which did not recognise the Government of Ireland Act, and was actively engaged in the Irish War of Independence. The Act was intended to deliver Home Rule in Ireland, with separate parliaments for Southern Ireland (which included three of the nine counties of Ulster) and Northern Ireland. Six of the thirty-two counties of Ireland were assigned to Northern Ireland, and the rest of Ireland comprising 26 counties to Southern Ireland.
Partition of Ireland
Since partition, a key aspiration of Irish nationalists has been to bring about a reunited Ireland, with the whole island forming one independent state. This goal conflicts with that of the unionists in Northern Ireland, who want the region to remain part of the United Kingdom. The Irish and British governments agreed, under the 1998 Belfast Agreement, that the status of Northern Ireland will not change without the consent of a majority of its population. In its white paper on Brexit, the United Kingdom government reiterated its commitment to the Belfast Agreement. With regard to Northern Ireland's status, it said that the UK Government's "clearly-stated preference is to retain Northern Ireland’s current constitutional position: as part of the UK, but with strong links to Ireland".