Rangers vs Celtic football has always been tied up with Ireland. In the 19th and 20th centuries, Glasgow filled up with Irish Immigrants of both Catholic and Ulster Protestant extraction, and they formed seperate football teams on sectarian lines. Throughout the Northern Irish troubles, Celtic has taken the republican side and Rangers the Loyalist side.
The rivalry has traditionally been the most violent in British football history. Even today, wandering into the wrong pub wearing the other team’s colours is a good way of getting yourself a bloody good hiding, if you’re lucky. Although things have calmed down quite a bit from how they were....
Well, isn’t that special!?!
I remember reading an article about the rivaly in Sports Illustrated around 1966 or so. Of course at that time most Americans not only knew little about football/soccer, they knew little about the religious problems affecting the Isles. I was generally surprised at the animosities revealed in the article as most of my close friends were Protestants and I was a Catholic. I might still have that magazine issue gathering dust in my basement.