Last class, we received a lecture on the Norther-Ireland/Ireland conflict. It was quite interesting, but a bit long, so most of the student lost attention and fell into their computer screens (including me, unfortunately).
The conflict is often seen as religious, however this is not really the case. It's ethnic and political: England was at war with catholic France and Spain(?), and the Irish could help them attacking England. They figured that if the French/Spanish kept arms and soldiers in Ireland, an invasion would be easier for them. Accordingly, they conquered Ireland.
Since then, there have been various conflicts in Ireland. The main causes for this are bad treatment - they lived in worse areas and didn't get good jobs. The potato famine fired up under the conflicts and gradually increased. Then came the war of independence in 1912, causing Ireland to gain home rule, while Northern-Ireland remained a part of the United Kingdom.
In Northern-Ireland the Catholics were still not treated as well as the Protestant population, which led to The Troubles. The conflicts developed into a full-scale civil war, between the IRA and the Unionists. This caused the Prime Minister of the UK to directly rule in Northern-Ireland, which at the time was Maggie Thatcher. She allowed captured IRA fighters to starve to death, because they wanted status as political prisoners, while she saw them as ordinary criminals.
Today things are stirring in Northern-Ireland again. There's no apparent cause for the conflict, except for the reconciliation. I have already written a note on this, you can read it here.