The caliphate was established as the succession to Muhammad and became a defining institution of Muslim societies. It was, however, an evolving institution with a different political and religious meaning in successive eras. The first phase, the period of the Rightly Guided Caliphs (632–61; known as Rashidun), was the religious chieftainship of a community and the political leadership of a coalition of nomadic conquerors. In the succeeding early Umayyad period (661–85), the caliphate was refashioned as a Syrian-Arab monarchy. In the later Umayyad (685–750), the caliphate was transformed into a new form of Middle Eastern empire defined and legitimized both in older imperial and in Islamic terms.

The Rightly Guided Caliphs

The bare outlines of the historical record suggest a very uncertain and contested beginning. At the death of the Prophet, there was no instruction from him and no agreement among his followers that there should be a succession at all. ʿUmar and other Muslims persuaded a partial gathering of the community to accept Abu Bakr as caliph. Abu Bakr (632–34), the first of the Rashidun caliphs, was named amir al-muʾminin (commander of the believers), a shaykh or chief who led the collectivity, arbitrated disputes, and followed the precedents set by Muhammad. His authority derived from tribal tradition, his personal connection to the Prophet, and the community's election of him. According to tradition, on assuming his office, Abu Bakr said simply that he would obey the precedent (sunna) of the Prophet and that people should obey him as long as he obeyed it.