Muhammad and his followers fled from Mecca to Medina in 622. In Medina, Muhammad’s Meccan followers and converts from Medina formed a single community of believers, the umma. During the last decade of Muhammad’s life, the umma in Medina developed into the core of the Islamic state that would later expand to include all of Arabia and lands beyond in Africa, Europe, the Middle East, and Central Asia. Muhammad’s father-in-law Abu Bakr took over leadership of the umma as the successor (caliph) of Muhammad. Abu Bakr faced two main tasks: standardization of the Islamic religion and consolidation of the Islamic state. Abu Bakr successfully re-established Muslim authority over the Arabs and oversaw the compilation and organization of the Quran in book form. Disagreements over the question of succession to the caliphate emerged following the assassination of the third caliph, Uthman. A civil war was fought between those who supported keeping the caliphate in Uthman’s clan (the Ummaya) and those who supported the claim of Muhammad’s first cousin and son-in-law Ali. The Umayya forces won and established the Umayyad Caliphate in 661. These disagreements led to the development of three rival sects in the Muslim community. The Shi’ites supported Ali’s claim to the caliphate and believed that the position of caliph rightly belonged to the descendants of Ali. Those known as the Sunnis believed that the first three caliphs had been correctly chosen and supported the Umayyad Caliphate. The most militant followers of Ali formed the Kharijite (rebel) sects. Most of the 800 million Muslims of today are either Sunnis or Shi’ites.