Muslims having trouble with Muslims. There’s some irony for ya’.
Apparently it all goes back to when Aisha, one of Mohammed’s wives, was suspected of adultery, and Ali urged Mohammed to divorce her. Aisha never forgave Ali and led the opposition to him when he became the fourth caliph, and the Sunni vs. Shi’ite enmity has raged ever since.
Actually, Muslims have killed more Muslims than anyone else.