Here, in the West of Scotland, we have a Catholic/Protestant clash. The feelings are similar to NI (due to mass immigration to here, from Northern Ireland and the Republic), but we don't have the paramilitary groups. There is hatred here, which raises its ugly head each time a football match is played between Rangers and Celtic. I say Catholic/Protestant, but, from experience, most people involved in the animosity toward the other side don't even attend church. I was raised Catholic, but I was one of very few in my class who went to mass every Sunday. The others in my class were 'Catholic' apparently and hated the 'Proddies', but they ridiculed me for going to mass and believing in God. They have children now and send them to the Catholic school, are raising them as Catholic, and still don't go to mass each week. I doubt very many of them even believe in God at all. It does seem to be a cultural/historical thing and really has very little to do with faith. Strangley, I'm the one who is a proclaimed agnostic now.
BTW Grebels, I don't think we can call the British, who ruled Ireland, Celts. That may be quite accurate where the Scots, Welsh and some English are concerned. But, as for the majority of the English (who are the largest group), a fair portion of their ancestry would have been Anglo-Saxon. Although I'm not sure of the significance of that.
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"We act as though comfort and luxury were the chief requirements of life, when all we need to make us really happy is something to be enthusiatic about." Charles Kingsley