A major Shī'ī Muslim community, the Ismailis have had a long and complex history dating back to the formative period of Islam, when different communities of interpretation developed their doctrinal positions. By the time of the Abbasid revolution in 132/750, Imāmī Shī'ism, the common heritage of the major Shī'ī communities of Ithnā'ashariyya (Twelvers) and Ismā'īliyya, had acquired a special prominence. The Imāmī Shī'īs, who like other Shī'ī communities upheld the rights of the Prophet Muḥammad's household (ahi al-bayt] to the leadership of the Muslim umma, propounded a particular conception of divinely instituted religious authority, also recognising certain descendants of the Prophet from amongst the ‘Alids as their spiritual leaders or imams possessing the required religious authority. The Shī'ī conception of religious authority, which set the Shī'a in general apart from the groups later designated as Sunni, came to be embodied in the central Shī'ī doctrine of the imamate expounded by the Imam Ja'far al-Ṣādiq and his associates. The doctrine of the imamate has retained a central position in the teachings of the Ismailis.

PHASES IN ISMAILI HISTORY

On the death of the Imam al-Ṣādiq in 148/765, his Imāmī Shī'ī following split into several groups, including those identifiable as the earliest Ismailis. The Ismailis themselves experienced several major and minor schisms in the course of their eventful history; the schisms normally revolved around the rightful succession to the imamate. By the middle of the 3rd/9th century, the Ismailis had organised a revolutionary movement against the established order under the Abbasids. In 286/899, the unified Ismaili movement was rent by its first major schism over the question of the imamate. The Ismailis now split into two rival camps, the loyal Ismailis and the dissident Qarmaṭīs. Upholding continuity in the Ismaili imamate, the loyal Ismailis acknowledged the founder of the Fatimid dynasty and his successors as their imams. The Qarmaṭīs, centred in Baḥrayn, did not recognise the Fatimid caliphs as their imams and in time they opposed the Fatimids. By the final decades of the 3rd/9th century when Ismaili dā'īs or religio-political missionaries were active from the Maghrib in North Africa to Transoxania in Central Asia, Ismailism (named after al-Ṣādiq's eldest son Ismā'īl) had received much popular support among different social strata.

The early success of the Ismaili da'wa or mission culminated in 297/909 in the establishment of an Ismaili dawla or state, the Fatimid caliphate, in North Africa.