The Protestants in Northern Ireland are the descendants of planters sent over from from Scotland during the Ulster plantation in the early 17th century. The British had attempted two similar plantations previously, one in the midlands and another in Ulster, but they tried to send English which resulted in an insufficient number of planters (Ireland seemed a long way from the Home Counties), so all the planters were slaughtered. The plantation of Ulster came shortly after the defeat of the O’Neills and O’Donnells of Ulster at the battle of kinsale (long story) and the fall of Gaelic Ireland’s last stronghold, Ulster, and the flight of the earls. The British had learned from their previous failed plantations so sent Scots this time, and Scotland to Ulster is but a stone throw (they were even one kingdom once upon a time called Dal Riada). So that’s what the real division is about in the north - the Protestants are British/Scottish who were sent to Ireland to make Ireland British, while the Catholics are native. It doesn’t really have anything to do with religion, but because the Irish and Scots have basically been the same people since Dal Riada the only way we can differentiate the nationalities is by religion. That’s why I say there’s no issues between Catholics and Protestants in the south, cos down here it’s just religion so it doesn’t matter. Whereas up north it’s the way to define if someone if British or Irish.