True, but it was crazy, I think finally a few years ago Rangers and Celtic finally allowed cross-sectarian players to play for them. You know how crazy that rivalry is and just how big of a deal it is.
Even though the two teams are based in Scotland, the vast majority of supporters are Irish immigrants, the Loyalists root for Rangers and the Catholics root for Celtic.
The same dynamic occurred in my hometown; as foreigners from outside the Islands of the North Atlantic (we Irish won’t say “British Isles”) inundated our area in NJ, it seems most have put their differences aside and are content to just be around people that speak the same language and eat the same food (the religion itself is moot, as many on both sides have dropped it altogether).
Many of the Irish moved to Scotland to take jobs during WWII, as Scots could be drafted while Ireland remained neutral. Plenty of those have since moved here; apparently Scotland is trying to lure both Scots and Irish back because young people don’t want to stay there.