Because there was a break down of law and order in Ireland. Catholics were being treated unfairly and protestants were outnumbering them. There was no talking of this situation in Parliament so the problem would never be solved.
The catholics and protestants were on the brink of civil war. Of course the border made in 1921 to separate northern Ireland and Ireland was only meant to be temporary however this just added to both catholics and protestants frustration. So of course the British troops had to be sent it, it was inevitable.
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.