The Government of Ireland Act finally introduced Home Rule to Ireland. But it also divided it, creating two separate states which laid the groundwork for the present conflict.
Under Unionist pressure, the new state was gerrymandered. Instead of the historic nine-county province of Ulster, the North was made up of the six largely Protestant counties of Antrim, Down, Armagh, Tyrone, Fermanagh and Londonderry/Derry. Donegal, Cavan and Monaghan were excluded because they would have given the balance of power to Catholics.
The Act of partition was never intended to be permanent. The Act states that "as soon as may be after the appointed day" the two states should establish a Council of Ireland to harmonise and ultimately unify the island under a "parliament of for the whole of Ireland".