When Muhammad died in 632, he left a large Muslim umma, but this community stood in danger of disintegrating into separate tribal groups. How was the vast empire that came into existence within one hundred years of his death to be governed? Neither the Qur’an nor the Sunna offered guidance concerning the succession.

In this crisis, according to tradition, a group of Muhammad’s ablest followers elected Abu Bakr (573–634), the Prophet’s father-in-law and close supporter, and hailed him as caliph, a term combining the ideas of leader, successor, and deputy (of the Prophet). This election marked the victory of the concept of a universal community of Muslim believers.

Because the law of the Qur’an was meant to guide the community, there had to be an authority to enforce the law, and the caliph assumed this responsibility. Muslim teaching holds that the law is paramount. God is the sole source of the law, and the ruler is bound to obey the law. Government exists not to make law but to enforce it. Religious leaders and institutions act as a check on political leaders who drift too far from religious standards. The creation of Islamic law in an institutional sense took three or four centuries and is one of the great achievements of medieval Islam.

In the two years of his rule (632–634), Abu Bakr governed on the basis of his personal prestige within the Muslim umma. He sent out military expeditions, collected taxes, dealt with tribes on behalf of the entire community, and led the community in prayer. Gradually, under Abu Bakr’s first three successors, Umar (r. 634–644), Uthman (r. 644–656), and Ali (r. 656–661), the caliphate emerged as an institution. Umar succeeded in exerting his authority over the Bedouin tribes involved in ongoing conquests. Uthman asserted the right of the caliph to protect the economic interests of the entire umma. Also, Uthman’s publication of the definitive text of the Qur’an showed his concern for the unity of the umma. However, Uthman was from a Mecca family that had resisted the Prophet until the capitulation of Mecca in 630, and he aroused resentment when he gave favors to members of his family. Opposition to Uthman coalesced around Ali, and when Uthman was assassinated in 656, Ali was chosen to succeed him.

The issue of responsibility for Uthman’s murder raised the question of whether Ali’s accession was legitimate. Uthman’s cousin Mu’awiya, a member of the Umayyad family who had built a power base as governor of Syria, refused to recognize Ali as caliph. In the ensuing civil war Ali was assassinated, and Mu’awiya (r. 661–680) assumed the caliphate. Mu’awiya founded the Umayyad Dynasty and shifted the capital of the Islamic state from Medina in Arabia to Damascus in Syria. Although electing caliphs remained the Islamic ideal, beginning with Mu’awiya, the office of caliph increasingly became hereditary. Two successive dynasties, the Umayyad (661–750) and the Abbasid (750–1258), held the caliphate.

From its inception the caliphate rested on the theoretical principle that Muslim political and religious unity transcended tribalism. Mu’awiya sought to enhance the power of the caliphate by making tribal leaders dependent on him for concessions and special benefits. At the same time, his control of a loyal and well-disciplined army enabled him to take the caliphate in an authoritarian direction. Through intimidation he forced the tribal leaders to accept his son Yazid as his heir, thereby establishing the dynastic principle of succession. By distancing himself from a simple life within the umma and withdrawing into the palace that he built at Damascus, and by surrounding himself with symbols and ceremony, Mu’awiya laid the foundations for an elaborate caliphal court. Many of Mu’awiya’s innovations were designed to protect him from assassination. A new official, the hajib, or chamberlain, restricted access to the caliph, who received visitors while he was seated on a throne surrounded by bodyguards.

The assassination of Ali and the assumption of the caliphate by Mu’awiya had another profound consequence. It gave rise to a fundamental division in the umma and in Muslim theology. Ali had claimed the caliphate on the basis of family ties — he was Muhammad’s cousin and son-in-law. When Ali was murdered, his followers argued that Ali had been the Prophet’s designated successor — partly because of the blood tie, partly because Muhammad had designated Ali imam (ih-MAHM), or leader in community prayer. These supporters of Ali were called Shi’a (SHEE-uh), meaning “supporters” or “partisans” of Ali (Shi’a are also known as Shi’ites). In succeeding generations, opponents of the Umayyad Dynasty emphasized their blood descent from Ali and claimed to possess divine knowledge that Muhammad had given them as his heirs.

Those who accepted Mu’awiya as caliph insisted that the central issue was adhering to the practices and beliefs of the umma based on the precedents of the Prophet. They came to be called Sunnis (SOO-neez), which derived from Sunna (examples from Muhammad’s life). When a situation arose for which the Qur’an offered no solution, Sunni scholars searched for a precedent in the Sunna, which gained an authority comparable to the Qur’an itself.

Both Sunnis and Shi’a maintain that authority within Islam lies first in the Qur’an and then in the Sunna. Who interprets these sources? Shi’a claim that the imam does, for he is invested with divine grace and insight. Sunnis insist that interpretation comes from the consensus of the ulama, the group of religious scholars.

Throughout the Umayyad period, the Shi’a constituted a major source of discontent. They condemned the Umayyads as worldly and sensual rulers, in contrast to the pious true successors of Muhammad. A rival Sunni clan, the Abbasid (uh-BA-suhd), exploited the situation, agitating the Shi’a and encouraging dissension among tribal factions. The Abbasids contrasted their own piety with the pleasure-loving style of the Umayyads.