Northern Ireland was formed from six of the nine counties of Ulster: four counties with  unionist majorities and two counties, Fermanagh  and Tyrone, which had slight Irish nationalist majorities. It was created as a separate legal entity on 3 May 1921, under the Government of Ireland Act 1920.

The first years of the new autonomous region were marked by bitter violence, particularly in Belfast. The IRA was determined to oppose the partition of Ireland so the authorities created the Ulster Special Constabulary to aid the Royal Irish Constabulary (RIC) and introduced emergency powers to combat the IRA. Many died in political violence between 1920 and 1923, during which Belfast experienced the worst violence in its history.

The origin of Northern Ireland lies in English colonial policy and activity in Ireland. It can be traced back to plantations of settlers in Ireland, in particular the Plantations of Ulster from 1606-1698. The defeat of the old Gaelic aristocracy in the nine-year war (1594-1603) was…