Islam has never been homogeneous since the generation after Muhammad. This has not generally led to much sectarian strife, except when geopolitical factors have intervened.

The present wave of fanaticism is primarily due to one man: Ronald Reagan. It all dates back to him funding the Afghan mujahideen as a Cold War strategy. Build an army of totally amoral thugs brutal enough to bring down the Soviet Union and it isn't going to go away or grow a spirit of tolerance any more than the Freikorps did after WW1.