Representing the second largest Shia community, the Ismailis have had their own complex history. The history and origins of Ismailis go back to the medieval times during which the Ismailis established states of their own on separate occasions, and for relatively long periods played crucial parts in the history of the Muslim world. During the second century of their history, the Ismailis founded the first Shia caliphate under the Fatimid caliph-imams. At the same time, they made important contributions to Islamic thought and culture during the Fatimid phase of their history.
Branches of Ismailis:
A schism that later took place, acted like a turning point in the history and origins of Ismailis splitting them into its two major Nizari and Mustaʿlian branches. The leaders of the Nizari branch succeeded in founding a cohesive state in scattered territories stretching from eastern Persia to Syria. The Nizari Ismaili state, comprised of numerous mountain strong- holds and towns, collapsed under the onslaught of the all-conquering Mongols in 654/1256. Thereafter, the Ismailis, belonging to the Nizari and Tayyibi Mustaʿlian factions, survived in many lands as minority Shia communities.
The Nizaris have continuously benefited from the guidance of their hereditary line of imams, who have acquired international fame since the middle of the 19th century under the title of Aga Khan. On the other hand, the Tayyibis, who have split into several groups, have been led by lines of daʿis while their imams have remained in concealment since 524/1130. There were also the radical Qarmatis, who split off from the Ismailis and founded their own state in eastern Arabia and engaged in hostilities with both the Shia Fatimids as well as the Sunni Abbasids. By the end of the 5th/11th century, however, the Qarmatis had disappeared from the historical stage.
As noted, much progress has taken place in modern times in the study of the Ismailis and their teachings. On the basis of the findings of modern scholarship, Ismaili history and thought may be conveniently studied in terms of a number of distinct phases.
Taken from: A History of Shiʿi Islam
By: Farhad Daftary