All religions. I agree with RR. You cannot restrict this phenomena to a certain religion. You want more. Within each religion you would find iron curtains. Among Muslims you would find this iron curtain between each of the Sunni, Shiia and Druze. Among Christains the same story would be between Catholics and Orthodox. In Europe you have former Yugoslavia as a good example.

===================================== http://www.qatarliving.com/node/58409