What is the Sunni-Shiite split and what caused it?

Answer 1

The Sunni-Shiite split is a doctrinal schism in Islam that occurred due to political disagreements over Succession after Muhammad's death. The Muslim community was united while Muhammad was the leader of this community. Most Muslims hold, however, that he never specifically chose a successor to his leadership. There was a minority in the community that supported the candidacy of 'Ali, the Prophet's son-in-law, this political faction became known as the "Supporters of 'Ali" which in Arabic is Shiat 'Ali (where the modern term "Shiite" comes from). They derived their support from specific hadiths and events that they claimed showed that God had revealed to Muhammad that 'Ali would succeed him. The majority of Muslims held that these hadiths and events showed nothing more than that 'Ali was very pious, something they did not deny. Therefore they gave power to the man who was Muhammad's second-in-command and father-in-law Abu Bakr. This majority were called the People of the Customs [of the Prophet] which in Arabic is Ahl Sunna (from where the modern term "Sunni" comes from.)

It is important to note that the split between the Sunnis and the Shiites was not the only split in Islam.