After 600 years of oppression, and several previous attempts (which coined the phrase "The fighting Irish - As they never lay down and accepted occupiers) the Irish revolted in 1916 to go on a defeat the British empire and force them to withdraw from the nation.
Humiliated, the British made an agreement to leave the Island, except for 6 northern counties to save face from absolute defeat. Ireland has been the thorn in Britains side for centuries.
The withdrawl was due to several reasons.
1/ International condemnation and pressure for their treatment of the Irish.
2/ The brittish were unable to control the Irish as every man in the street was willing to lay down his life for his country and his freedom.
3/ The losing battle they were fighting on the streets of Dublin and towns around the country was humiliating for an "Empire".
Irelands population was once peaked at 12 million in the 1800's.... a century on, the Irish population is 3.5 million.
This is due to brittish rule forcing famine around the country in which millions of innocent people starved to death or died of the plague and hundreds of thousands of others were forced to emigrate, mostly to the USA, Australia and Argentina.
After the Brittish left, the Irish fell into civil war over the agreement to let them leave and keep the 6 counties. Some were for this, as the Brittish were fucking off, some were against...