As usual, Big Tim has it right. You could look a lot and not get a more concise short description of how it goes. The history has many twists and turns. One correction, Uncle Dave. The Rising of '16 could hardly be described as a success. The leaders of '16 were beaten and badly. It was only the excesses of the British in executing them, among other things, that caused world opinion to shift in favor of the Irish Nationalists. This had the effect of breathing air into the rebels. The reference to WW1 is a bit erroneous as well. While it is true that the rebels had intended to use the fact that the British were "otherwise preoccupied", the British negotiators stretched it out to the end of WW1. They then were able to shift troops to this struggle. The armistice in Europe occurred in late 1918. The truce was called for by King George in 1921. The IRA at that point was near collapse.

All the best,

Mick