Answer:
B the death of Muhammad
Explanation:
It is widely believed that Prophet Muhammad helps the unification of various groups or tribes in the Arab world during his lifetime.
However, following his death on June 8th 632, there was disagreement over the method of selection and qualifications for caliph in early Islamic society.
The majority who are referred to as Sunnis believed that Caliph should be selected through election or community agreement. While the Minority often referred to as Shi'a believed that it is only God that select Caliph and not just mere humans.