[1066AD]

Britain ruled Ireland for some few hundred years .. sixteenth century if not before. Irish independence was granted after WW1 but the six counties of Ulster were partitioned off to remain in UK as the majority was of protestant Scottish descent, the British gov't having encouraged immigration over the previous two or three hundred years.
The IRA was banned in the Irish Republic (Eire) but re-emerged in the 60s, armed by Libya etc. Their goal is still, as far as I know, a marxist republic encompassing the whole island.
The majority in Northern Island (Ulster) still wants to stay in UK (a majority which includes many catholics), one reason being the UK welfare state bennies are better.

[elmer fudd]

Actually there are nine counties in Ulster and three of them are part of the republic.