What many blame about the Islam religion and about Muslims divisions ... the same happened for Jews and Christians before.
Divisions of Jews
were evident even in the time of Moses himself, and people murmured and rebelled, and when he left them for forty days, they divided into two parties: those who worshiped the calf, and others the believers who remained steadfast with Aaron to worship God alone and reject the idolatry.
While after Moses their history is full of divisions and schisms.
The Book of Judges and other books of the Torah collection is full of such examples.
Their Rebellion against Their Prophet
Their Hearts Were Hardened
In the above link, see the wars and fighting between brothers and cousins with tens of thousands of killed victims among them.