Partition of Ireland
The Government of Ireland Act 1920 took effect, dividing Ireland into Northern Ireland (six counties of Ulster) and Southern Ireland. Northern Ireland's boundary was drawn to secure a Protestant and Unionist majority who wished to remain part of the United Kingdom, while the mostly Catholic and nationalist south moved toward independence. The settlement left a large nationalist minority inside Northern Ireland who did not accept the new state. This division set the stage for decades of communal tension.