From the split of the Sunni and Shi’a, to the branches of Shi’a communities, Dr. Daftary provides an overview of the evolution of branches of Islam.  

The historical formation of the worldwide Muslim community or Ummah, as it is known in Arabic, has resulted in a great deal of diversity that reflects a rich intellectual, spiritual, and institutional pluralism. During his lifetime, Prophet Muhammad was both the recipient and expounder of divine revelation. For Muslims, his death in 632 CE marked the conclusion of the line of prophecy and the beginning of the debate over the nature of his legacy for future generations.
Modern scholarship has shown that during the first three centuries of Islamic history, Muslims lived in an intellectually dynamic and fluid milieu characterized by a multiplicity of communities of interpretation and schools of thought, with a diversity of views on a wide range of religio-political issues. The early Muslims were confronted by many gaps in their religious knowledge and understanding of the Islamic revelation, which revolved around issues such as the attributes of God, definition of what it meant to be a believer, and the nature of religious authority after the Prophet, amongst other theological concerns. It was during this formative period that different groups and movements began to elaborate their doctrinal positions and gradually acquire their distinctive identities and designations that often encapsulated central aspects of their belief systems.

Islam after the Prophet Muhammad

The origins of Sunni and Shi‘a branches of Islam, can be traced to the differing views over the succession to Prophet Muhammad. After the Prophet’s death, a successor was needed to assume the leadership over the Ummah. A group of Muslims held that the Prophet’s cousin and son in-law, ‘Ali b. Abi Talib, had been designated by the Prophet as his successor under divine command and that he was, therefore, the best candidate to succeed the Prophet.  This group expanded and became designated as the Shi‘at ‘Ali, “party of ‘Ali”, or simply as the Shi‘a. 
Most of those who held that the Prophet had not designated a successor, endorsed the historical caliphate of a close companion and father-in-law of the Prophet, Abu Bakr, and eventually coalesced into the majoritarian, Sunni branch of Islam, known collectively as the ‘People of the Sunna and Consensus, ahl al-Sunna wa al-jama‘a.
In time, Sunni religious scholars (‘ulama) articulated the notion of the khulafa al-rashidun, or the Rightly Guided Caliphs, as being the rightful leaders over the Muslim world. They promoted the precepts of Sunni Islam as reflecting “true” Islam from which other groups had deviated. Non-Sunni Muslim communities, including the Shi‘a, were therefore considered to have deviated from the right path, and they were at times accused of heresy (ilhad), innovation (bid‘a) or even unbelief (kufr). 

The Shi’a Interpretation 

The Shi‘a also elucidated their own paradigmatic model of ‘true Islam,’ rooted in a particular interpretation of early Islamic history and a distinctive conception of religious authority vested in Prophet Muhammad’s family or the ahl al-bayt.
While affirming, in common with their fellow Muslim believers, the Shahada, or belief in the unity of God and the model of divine guidance through God’s Messenger, Prophet Muhammad, the Shi‘a maintain that for the spiritual and moral guidance of the community, God instructed the Prophet to designate a figure of authority to succeed him as leader of the Muslims. This authority was Imam ‘Ali. 
According to the Shi‘a, this conception of the community’s future leadership was made public by the Prophet in the final year of his life at Ghadir Khumm, where he designated ‘Ali as his successor to lead the Muslims. While both Shi‘a and Sunni sources refer to this event, it is the specific interpretation of the role of Imam ‘Ali as the Prophet’s successor, or wasi, that distinguishes the Shi‘i interpretation of authority and leadership from those of other Muslim communities.

A Need for Ongoing Guidance

The Shi‘a maintained that while revelation ceased at the Prophet’s death, the need for the spiritual and moral guidance of the community, through an ongoing interpretation and implementation of the Islamic message, continued. They believed that the legacy of Prophet Muhammad was entrusted to the designated members of the Prophet’s family, or the ahl al-bayt, who had the sole prerogative of expounding the precepts and practices of lslam. The Shi‘a held that after Imam ‘Ali, the leadership of the Muslim community, was the right of the ‘Alids, the descendants of Imam ‘Ali, especially through his sons by the Prophet’s daughter Fatima al-Zahra. 
The earliest Shi’i ideas and currents of thought found their full formulation and consolidation in the central Shi‘i doctrine of the Imamat. Over time, the Shi‘a disagreed among themselves regarding the identity of the ‘Alid Imams, leading to internal divisions within Shi‘i Islam.

Shi’a Identities

In the first few decades, the Shi‘a comprised mainly of Arab Muslims. As the Islamic empire expanded into non-Arab lands under the Umayyads, the so-called mawali, or non-Arab converts to Islam, were particularly drawn to Shi‘i Islam. As such, they played a key role in transforming Shi‘ism from an Arab party of limited membership and doctrinal basis, to a dynamic movement. Henceforth, different Shi‘i communities and other groupings, consisting of both Arabs and mawali, came to coexist, each with its own line of imams and elaborating its own ideas.
It was under such circumstances that Shi‘i Islam in the later Umayyad period developed mainly in terms of two branches or trends, the Kaysanis1 and the Imamis.  Another ‘Alid movement led to the foundation of a third major Shi‘i community, the Zaydis. By the end of the Umayyad period in 750 CE, the bulk of the Kaysani Shi‘is had transferred their allegiance to the Abbasids, descendants of the Prophet’s uncle ‘Abbas.  ‘Abbas had been initially conducting their anti-Umayyad campaign on behalf of an anonymous member of the ahl al-bayt, which held broad Shi‘i appeal.
The Imami branch, the early common heritage of the Ismailis and the Ithna ‘asharis, had acknowledged a particular line of ‘Alids, the descendants of Imam Husayn b. ‘Ali, as their imams, and they abstained from political activism. It was with Imam Muhammad al-Baqir (d. 732), that the Imami branch of Shi‘i Islam began to acquire prominence. 
During the long and eventful imamate of Imam al-Baqir’s son and successor, Imam Ja‘far al-Sadiq, the Imami Shi‘i expanded significantly and became a major religious community with a distinct identity. As a result of the wide-ranging intellectual activities of Imam Ja‘far al- Sadiq, who was one of the foremost scholars of his age, the Imami Shi‘is propounded distinctive theological and legal doctrines. In particular, they elaborated the doctrine of the imamate, which was essentially retained by later Ismaili and Ithna ‘ashari Shi‘is. The last Imam recognized by both the Ismailis and the Ithna ‘asharis, Imam Ja‘far al-Sadiq, died in 765. The dispute over his succession led to historic divisions among the Imami Shi‘a, marking the emergence of the earliest Ismailis, whose history will be discussed in the Part 2 of this article.
1 Kaysanis believed that the family of the Prophet included not only the descendants of Imam ‘Ali and Fatima al-Zahra, but other members of the Banu Hashim. In 686, al-Mukhtar claimed that Muhammad ibn al-Hanafiyya (d.700), a son of Imam ‘Ali and a half-brother of Imam Husayn was the Mahdi and he would return before the day of Judgement to restore true religion and justice.
2 Zaydis consider Zayd ibn ‘Ali, another son of the Imam Zayn al-‘Abidin as their Imam. They believed that descent from the family of the Prophet was essential for being the rightful ruler, but it was not enough by itself. This leader also needed to have other qualities such as being able to launch an active revolt against the unjust rulers.