The caliphate arose out of the death of Muhammad in 632 CE and the subsequent debate over the succession to his leadership. Abu Bakr, a close companion of Muhammad from the Banu Taym clan, was elected the first Rashidun leader and began the conquest of the Arabian Peninsula. He ruled from 632 to his death in 634. Abu Bakr was succeeded by Umar, his appointed successor from the Banu Adi clan, who continued the conquest of Persia, eventually leading to the fall of the Sasanian Empire in 651. Umar was assassinated in 644 and was succeeded by Uthman, who was elected by a six-person committee arranged by Umar. Under Uthman began the conquest of Armenia, Fars and Khorasan. Uthman was assassinated in 656 and succeeded by Ali, who presided over the civil war known as the First Fitna (656–661). The war was primarily between those who supported Uthman's cousin and governor of the Levant, Muawiyah, and those who supported the caliph Ali. The civil war permanently consolidated the divide between Sunni and Shia Muslims, with Shia Muslims believing Ali to be the first rightful caliph and Imam after Muhammad. A third faction in the war supported the governor of Egypt, Amr ibn al-As. The war was decided in favour of the faction of Muawiyah, who established the Umayyad Caliphate in 661.