Haha, do you have a few years?
Read this if you want the full, and accurate, story
http://en.wikipedia.org/wiki/The_Troubles
Ok England conquered Ireland many many years ago, back in the days of Oliver Cromwell if I recall correctly, maybe even before that. The English didn't necessarily treat the Irish all that well, kinda gave the good land to rich Lords and the Irish basically became peasants, dependent on the potatoes they grew for food, which is why they got hit so hard when Blight hit the potatoes, causing the famine. The English didn't really handle things all that well, and a particular band of thuggish soldiers known as the black and tans caused a lot of grief, particularly to the catholic community, which was the majority in the south. So the catholics weren't happy with English rule, which led to several uprisings like the Easter Uprising in 1916. Then the IRA started their guerilla warfare in 1920 against the English (led by Michael Collins, an absolute genius tactician). So thats where the IRA (Irish Republican Army) came from, honorable enough to begin with. They wanted a republic, free from British rule. The Loyalists (mostly pro-*test*-('")ants) in the Northern counties wanted to stay under British rule because they were doing all right out of it economically, and were worried this would change. So THEY formed the UVF (Ulster Volunteer Force). Interestingly enough, both the IRA and the UVF fought for Britain in World War I, both hoping to gain favour from the UK government.
Anyways, a lot of stuff happened, and eventually the English decided it would be best to try and give them both what they wanted, so they created the Free State (what became Southern Ireland) as a temporary measure, and let the pro-*test*-('")ant majority in the North keep most of the region of Ulster, what has now become Northern Ireland. The idea was that after a while there would be a unite Irish republic eventually. But then the Northern Loyalist politicians started fighting to keep the North under British rule, and the Republican politicians started fighting to get a united Ireland. Then in the 60's, both sides started to get violent. In the 70s it got REALLY violent, and when u have some terrible acts being commited by both sides suddenly its not so much about the noble causes you were fighting for to begin with, but the resentment and sheer hatred for the other side and what THEY'V done that keeps the fighting going. Somewhere along the line, both sides have become like Mafia gangs and all they care about is drug money. They both had politicians fighting for them in parliament (although some of the republican politicians are known ex-IRA murderers, which makes it kind of hard to trust them!), and now these politicians have now formed a shared government in Northern Ireland (stil under British rule), so we'll see how it goes.
Obviously theres a lot more to it than that, and there have been some really terrible attrocities committed by terrorists on both sides. But theres been no big bombs since 1997 (the Omagh bomb, the IRA planted a car bomb in one end of the town, told the police it was at the OTHER end of the town, so the cops evacuated everybody right into the bomb), and none in recent years. So yeah, I guess it got to the stage where both communities hated each other, but couldn't really remember why.. and suddenly instead of terrorist organisations you had large drug gangs.
BUT, to be honest beside the Omagh bomb and a few in London nothing big has really happened that I can remember in my lifetime, and the majority of people now just want to get on with it and nuild up our country. You still have your hardliner thugs who want to cause trouble, but you have that everywhere, and here most people are just too fed up to listen to them anymore!
Anyways, thats a Brief (and probably grossly incorrect) History of the Troubles in Ireland! To summarise... Catholics Vs Pro-*test*-('")ants, nobody won, everybody lost, crowd got bored and went home, and now its perfectly safe for tourists to come and enjoy our beautiful country (no, really, its gorgeous). So come to Northern Ireland, bring your friends and their money!