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.
Dioceses of Ireland
The pre-Reformation Christian church in Ireland was first divided into dioceses at the Synod of Ráth Breasail in 1111, although the dioceses of Dublin and Waterford were founded earlier by Hiberno Norse rulers with bishops consecrated by the Archbishop of Canterbury in England. The boundaries were reconfigured at the Synod of Kells in 1152 into 37 dioceses. A few were later abolished, as when Glendalough merged Dublin in 1214–16.