The Nizari Ismailis are the largest segment of the Ismaili Muslims, who are the second-largest branch of Shia Islam after the Twelvers. Nizaris, along with Twelvers, adhere to the Jaʽfari school of jurisprudence. The Aga Khan, is the spiritual leader and Imam of the Nizaris. The global seat of the Ismaili Imamate is in Lisbon, Portugal.
The Nizari Ismailis have had their own complex history and separate doctrinal development. The circumstances of the early Nizaris of the Alamut period were radically different from those faced by the Ismailis of the Fatimid state and the Tayyibis of Yaman. From early on, the Nizari Ismailis who had broken away from the Fatimid regime, were preoccupied with a revolutionary campaign and their survival in an extremely hostile environment. Accordingly, they produced military commanders rather than highly trained daʿis and scholars addressing different intellectual issues.
The Nizaris of Persia had successfully struggled against too many formidable adversaries and for too long, and they were finally overwhelmed by the all-conquering Mongol armies led by Hülegü. In Syria, the Nizaris attained the peak of their power and fame under their most eminent daʿi Rashid al-Din Sinan (d. 589/1193), who successfully adopted complex and shifting alliances with the Ayyubids and other Muslim rulers as well as the neighbouring Crusaders. The Syrian Nizaris were spared the Mongol debacle. However, by 671/1273, all the castles of the Syrian Nizaris had fallen into Mamluk hands. The Nizaris of Syria were permitted to remain in their traditional abodes as loyal subjects of the Mamluks and the Ottomans, but much of their literary heritage was lost in prolonged conflicts with the neighbouring Nusayri (ʿAlawi) community.
The Nizari communities, are scattered from Syria to Persia, Central Asia and South Asia, now espoused a diversity of religious and literary traditions in different languages. Modern scholarship in Ismaili studies distinguishes three periods in the post-Alamut phase of Nizari history: an obscure early period covering the first two centuries; the Anjudan revival in the daʿwa and literary activities, and the modern period dating to the middle of the 13th/19th century when the residence of the Nizari imams was transferred from Persia to India and then to Europe. Numbering some 10 million, the Nizari Ismailis have emerged as progressive Shiʿi Muslim minorities in more than twenty-five countries of the world, and in every country of Asia, the Middle East, Africa, Europe and North America where the Nizari Ismailis live as religious minorities and loyal citizens, they generally enjoy exemplary standards of living while retaining their distinctive religious identity.