Reasons of division
Islam is the religion which Muslims follow and it was revealed by the last messenger of Allah, prophet Muhammad. After the death of prophet Muhammad, Muslims were divided into two major groups the Shias and Sunnis. This division further expends and today there are 72 sects in Islam, because of this division Muslims faced many challenges throughout the history. Today we will discuss some of the possible reasons which causes the division.
The Muslims at the time of prophet Muhammad were united and the followers of a single leader the prophet himself and the prophet was not only the religious leader but the ruler also. After the death of prophet both of the seats were vacant and the selection of the heir of prophet was the first reason which causes distribution. One group(Sunni) elected the close companion of prophet Abu Bakr as their first caliph, meanwhile on the other hand the second group(Shia) accepted the right of Ali (the son-in-law and cousin of prophet) as the heir of both positions. The reference of the appointment of Ali as heir of prophet given by Shia is when prophet was returning from the last plagiarism, he stopped at the place of Ghadeer and in the presence of one lac twenty five thousand people, he declared Ali as his heir by saying that "the one who accept me as master, Ali is his master".
After that Ali's follower accept his religious authority and on the other hand Abu Bakr, than Umar and Uthman succeeded him as rulers and after Uthman's death when Muslims were in tough times, Ali succeeded him as forth caliph and after the martyrdom of Ali in the mosque of Kufa, the conditions went from bad to worst and the divisions continues.