Big Mick's correct on that score, bubblyrat. I think it was around 1930 (or perhaps that very year) when both Catholic and Protestant workers went on strike together over the conditions they were expected to work for under the fat cat bosses (mainly protestant). It was a short-lived strike, as the capitalists, alarmed at the unusual show of solidarity, were quick to forment sectarian division. The usual way to do this was to slightly favour one side (prod) with slightly better conditions and then tell them to 'watch their backs' of those scummy Papists (Catholic) will have the shirt off yer"
In that way they drove the communities apart by giving one lot reason to be fearful over their privilege' (scraps from the master's table) while giving the other lot reason to be envious and resentful. Not much has changed these days, I think, in or out of the North. It takes an alert mind to spot it and resist it.
There were historic divisions of course, the ancestors of today's unionists arrived as protestant and presbyterian colonists from Scotland and England to supplant the native catholic who were regarded as 'disloyal'. That happened from the time of Henry VIII onwards. This was an injustice of course, but it must be borne in mind that some of the Catholic native chieftans were not very just either and occasionally acted as little tin-pot autocrats. A major difference was that under the Gaelic legal system the chieftan was leader for life but, while he and his family had use of the lands while he was alive, his family could not inherit it. This did not suit the Anglo-Norman system of primogeniture where the first son inherited all, 'making legal bastards of the rest of the family' as Thomas Paine put it. This way suited the Normans as it ensured the feudal system of loyalty survived through the generations. On the other hand the Irish chieftans had no legal right under Gaelic law to surrender their lands to the English Crown as they were not theirs to dispose of in that manner. In any case, in the late 19th century the Irish were able to buy back most of the land they had been dispossessed of, under a series of land reform acts. In some cases, the payments were still being made to the English Crown in the 1960s.
For what it's worth, Ireland has the 'distinction' of being the first country to be colonised by another European power in the so-called Age of Discovery, that time in the 1500s when European countries began to send ships across the Atlantic and around the world etc., We went through the whole cycle of conquest, dispossession, genocide (yes, genocide) etc., to finally wind up in the 1990s and 21st century talking round the table. So, McGrath of Harlow has a good point, Israel and Palestine can learn from our example, they'll probably end up at the same point eventually anyway.