What caused the split between Sunni and Shi'ia Islam?

The split between Sunni and Shi'ia Islam primarily stems from disagreements over rightful leadership following the death of the Prophet Muhammad in the 7th century. After his passing, there was significant debate among the Muslim community regarding who should be the rightful successor, or caliph.

Sunnis argue that the community should select their leader, which led to the acceptance of Abu Bakr, a close companion of Muhammad, as the first caliph. On the other hand, Shi'ites believe that leadership should remain within the Prophet's family and that Ali, Muhammad’s cousin and son-in-law, was the rightful successor. This foundational disagreement over leadership led to different interpretations of Islamic teachings and practices, establishing a distinct religious and theological identity for both sects.

Understanding this historical context clarifies why issues around leadership and authority are central to the Sunni-Shi'ite divide, rather than differences in religious texts, geographical divisions, or cultural variations, which while present, are not the fundamental cause of the schism.