Islam has Shiites and Sunnis; they're the two main groups fighting each other over in Iraq at the moment. The difference has to do with who are the "real" descendants of Mohammed. Everyone was happily agreeing but then technicalities arose and you get weird sects arising like Twelver Shiites who argue about the 12th successor/descendant "inman" only, think he's still "alive" and going to come back.

http://hnn.us/articles/934.html