The Prophet Muhammad left no successors when he died. The elders of the Muslim community elected Abu Bakr as the first khalifa, or caliph (literally, “successor” or “deputy”). This marks the beginning of the dispute between Sunni and Shi`a, the two main branches of Islam. As supporters of Ali, cousin and son-in-law of Muhammad, the Shi`a maintained that the caliph must be a descendant of the Prophet, and they opposed the success of Abu Bakr. Among the Sunni, however, Abu Bakr and his successors—Umar, Uthman, and Ali—are known as the “Rightly-Guided Ones,” signifying their election by popular consent. When the third caliph Uthman was murdered in CE 656, the Shi`a/Sunni dispute developed into a civil war that was not quelled until the assassination of Ali and assumption of power by the Umayyads in CE 661. A second war broke out in CE 680 upon the dealth of Ali’s son Husayn, who was leading a revolt at Karbala (Iraq) against the Umayyad caliph. Husayn’s martyrdom served to institutionalize the Sunni-Shi`a political split. It also gave rise to a distinctly Shi`a religious philosophy emphasizing the Imam (religious leader o the community), self-sacrifice, and martyrdom.

While the initial split began over the issue of the caliphate, the difference between Sunni and Shi`a has developed into a philosophical dispute over the nature of the imam. The Sunni believe that the imam should be chosen through consensus of the community. The Shi`a hold that the imam must be a descendant of Ali, who bestowed special knowledge from the Prophet on all of his descendants, rendering them infallible. Most Shi`a believe in a Hidden Imam who did not die, but went into hiding and will remain hidden until his reappearance at the end of time as the Mahdi (Guided One).

There are many branches of both Sunni and Shi`a Islam. Some of the more well known are briefly described below:

Sunni branches
The Khariji`i were the first group to break with the larger Islamic community in CE 658. Believing in absolute purity of conduct and belief, the Khariji`i attached everyone they considered an apostate. They exist today in small groups in North Africa and southern Arabia.

The Muwahhidun (Wahhabis) adhere to the teachings of Ibn Taimiya condemning all innovations in Islam. These teachings were adopted as the official doctrine of Arabia by the Sa`ud family in 1803.

Shi`a branches
The Imami (Twelvers) believe that the twelfth Imam after Ali is now hidden. The Imami are the dominant branch of Shi`a Islam and are found in Iraq, Syria, Lebanon, and especially Iran, where they form the majority. This branch of Shi`a Islam was made the official religion of Iran at the beginning of the Safavid Dynasty in 1501.

The Ismaili (Seveners) came to power in Egypt during the Fatimid Dynasty in the tenth century and believe in only seven Imams following Ali. Various small groups of Ismaili are found today in Syria, Iran, Afghanistan, India, Yemen, and East Africa, but their precise numbers are difficult to establish.

The Alawite of Syria and the Druze, found mainly in Lebanon, Israel, and Syria, are thought by many to be offshoots of the Ismaili. The Druze community was closed to outsiders in 1043 and the details of their doctrine remain secret, but it is generally believed to be a movement that grew up around the Fatimid Caliph al-Hakim, who proclaimed himself divine in 1017. Its relationship to Islam is mostly historical, as the Druze diverge greatly from mainstream Islamic believe and practice.

The Zaidi accept five Imams after Ali, ending with Zaid ibn Ali, but they do not accept the concept of the Hidden Imam. They are found in Yemen, where they established a state in the beginning of the tenth century.

Sufis