Why is Ireland split into two states?Watch
The Kingdom of Ireland, which was part of a personal union with Great Britain under the same monarch, joined the United Kingdom in 1801. Particularly in the early 20th century, there was support for Irish devolution within the UK and then for a separate Irish state - however, particularly in the north, there was clear opposition to both. The UK Government sought a compromise, creating two devolved parliaments in Northern and Southern Ireland in 1920. Irish nationalists won decisive election victories in the south, while the north was dominated by unionists.
In 1922, the UK agreed with the creation of an Irish Free State, which would continue to have the British monarch as head of state. Northern Ireland's parliament opted out, carrying on as part of the UK. Eventually at the end of the 1940s, the Irish Free State became a republic.