There was always conflict. The Muslim sects split along pretty much the same tribal lines that have been engaging in internecine warfare for the last few thousand years.
The only difference between then and now is, instead of fighting because the other guys are in the wrong blood tribe, they fight because the other guy "doesn't worship Allah the right way.
If you go back to before the advent of Islam, you'll find it's pretty much the same groups killing each other today.
