As Shiism spread over time and space it became culturally diverse. This enriched Shia life and thought and added new dimensions to the faith’s historical development that went beyond its roots in the Arab heartland of Islam. The practice of the faith itself adapted to new cultures as its message spread eastward from the Arab lands to Iran and India. Succession crises through the ages led to offshoots that broke away from the main body of Shiism—also known as Twelvers, for recognizing twelve imams. Following the death of the fourth imam in the eighth century; a minority followed one claimant to the imamate who rose in rebellion against the Umayyads. They are known as Zaydis (named after Zayd ibn Ali), or Fivers, for following only five imams. Today most Zaydis live in Yemen and are closer to Sunnism in their practice of Islam.

A graver schism occurred after the death of the sixth imam, the law codifier Jafar al-Sadiq, in 765 C.E. Jafar’s eldest son, Ismail, had died before his father. A group of Shias claimed that Ismail had inherited his father’s religious charisma while both men were still alive. Others disputed this and located the succession in a living younger son. Those who affirmed the charisma of Ismail came to be known as Ismailis or Seveners, for breaking off from the main body of Shiism after the seventh imam.

Ismailis remained a small denomination, but one that accentuated the cult of the imams and emphasized their function of revealing the inner meaning of Islam. They had an esoteric bent and became immersed in philosophy and mystical practices, eventually breaking with some of the fundamental teachings of Shiism and even Islam. In the tenth century, Ismailis rose to power in Egypt and founded the Fatimid dynasty (909–1171). The Fatimids left an imprint not only on Cairo’s Islamic architecture but also on Islam in Egypt, where the level of special devotion to the Prophet’s family is more intense than anywhere else in the Sunni world. The Ismailis also produced the cult of the Assassins in the twelfth century, when Ismaili warriors terrorized Iran’s then Sunni leadership.

The descendants of Ismail and the Fatimids continue to serve as living imams of that community. The current imam is Prince Karim Aga Khan, who looks after his community’s welfare from his seat in Paris. Ismailis pay tithe to the Aga Khan, who in turn oversees his flock, guiding them in religious matters as well as ensuring their material prosperity. The Aga Khan has built universities, schools, and hospitals in Ismaili communities and used his influence with kings and presidents, generals and businessmen to further the interests of Ismailis wherever they live.

There are Arab Ismaili communities—for instance, in the remote Najran province of Saudi Arabia—but in recent centuries Ismailis have largely been an Indo-Iranian community. Most Ismailis have traditionally lived in a circular pattern of settlement that runs from India into western China, Tajikistan, Afghanistan, northeastern Iran, and back down into Pakistan. The fall of the Soviet Union and certain openings in China have allowed the Ismailis to form renewed ties across this vast arc and the many international borders that it traverses. Under the British Raj, India’s Ismaili merchants did well and often migrated along imperial trade routes. Many settled in British East Africa and formed the merchant classes of Kenya, Tanzania, and Uganda. Africanization campaigns in that region in the 1970s—the worst one was part of the reign of terror that gripped Uganda under the dictator Idi Amin—sent many Afro-Indian Ismailis into exile. Some went to the United States or Britain, but most migrated to Canada. Over the centuries Ismailis have spun off smaller communities, including the Bohras of India, and have deeply influenced other small offshoots of Shiism, such as the Druze of the Levant, the Yezidis of Iraq, and the Alawi of Syria and Alevis of Turkey.