Shii Muslims, the followers or party of Ali , believe that Muhammad 's religious leadership, spiritual authority, and divine guidance were passed on to his descendants, beginning with his son-in-law and cousin, Ali ibn Abi Talib, his daughter, Fatimah , and their sons, Hasan and Husayn . The defining event of Shiism was the martyrdom of Husayn, his male family members, and many companions at Karbala (Iraq) in 681 by the Umayyads, granting an element of passion and pathos to Shiism.
There are three main branches of Shiis today: the Zaydis, the Ismailis (Seveners), and the Ithna Asharis (Twelvers or Imamis). The Zaydis (followers of Zayd ibn Ali ibn al-Husayn ) are located in Yemen, Iraq, and parts of Africa. They represent the activist groups who believe that the imam ought to fight for his rights and be a ruler of state. The Ismailis (Seveners) are named after the seventh imam, Ismail . They founded the Fatimid Empire ( 909 – 1171 ) and represent esoteric Shiism. The Ithna Asharis (Twelvers or Imamis) are the largest and most moderate group. They believe in twelve imams, beginning with Ali and ending with Muhammad al-Mahdi , who went into occultation and is expected to return at the end of time as the messianic imam who will restore justice and equity on earth. He is therefore referred to as the imam al-muntazar, the expected or awaited imam.
Historically, the Shiis enjoyed the most favorable conditions under Buwayhid rule ( 945 – 1055 ) in Baghdad and Iran. During this period, major collections of Shii hadith were compiled and Shii legal thought was formulated. Two popular Shii commemorations were instituted in Baghdad at this time: the remembrance of the martyrdom of Husayn on the tenth day of Muharram and the festival of Ghadir al-Khumm, commemorating the Prophet's nomination of Ali as his successor, on the eighteenth day of Dhu al-Hijjah. It was also at this time that public mourning ceremonies for Husayn were initiated, shrines were built for the imams, and the custom of pilgrimage to these shrines was established at the popular level. Scholars of the Mongol, Safavid, and Qajar periods also made major contributions to Shii literature, philosophy, theology, and law.
Shii political thought entered its modern phase during the Iranian Constitutional Revolution of 1905 – 11 , when Shiis were divided between the forces of constitutionalism, modernism, reason, and secularism, on one hand, and more traditional interpretations of faith, religious law, and the role of clerics, on the other. The clerical establishment ultimately joined with secular revolutionaries in opposing European colonialism. By the 1940s and 1950s Shii political thought was addressing issues such as Communism and nationalism, often presenting Shiism as an alternative. During the 1960s the institutional bases for the propagation of modern Shii political thought were formed through Quranic schools and voluntary associations of Muslim university students and professionals. Informal gatherings led by clerics and intellectuals also promoted Shii political mobilization. The most important event of the 1960s was the 1963 uprising led by Ayatollah Ruhollah Khomeini (d. 1989 ), who called for the ouster of the shah.
The most effective ideologue of modern Shiism was Ali Shariati (d. 1977 ). In the late 1960s and 1970s Shariati combined Islam with Third Worldism and revolution into an activist political ideology. He identified Western imperialism, cultural colonialism, social injustice, and political repression as the greatest contemporary challenges. In contrast to the passive, suffering role typically assumed by Shiis, Shariati cast Shiism as activist, radical, revolutionary, classless, and opposed to tyranny and repression. Shariati inspired the Iranian clerics Ayatollah Khomeini , who emerged at the head of the Iranian Islamic revolution, and Imam Musa al-Sadr (d. 1978 ), who encouraged the Shiis of Lebanon to take an activist role in struggling for better socioeconomic conditions and political representation.
Khomeini was the most rhetorically successful revolutionary Shii. Opposed to the increasing secularization of Pahlavi society and American domination of Iranian political, social, economic, and cultural life, Khomeini introduced the principle of vilayat-i faqih as the foundation for Islamic government. According to this principle, in the absence of an imam, the leadership of Muslim nations is to be entrusted to Shii jurists, who are to rule by virtue of their knowledge of sacred law and their ability to regulate the daily affairs of Muslims. The resultant Islamic revolution of 1979 and constitution of the Islamic Republic of Iran represent the ideological institutionalization of modern Shii political ideas. In the postrevolutionary period, such reformist thinkers as Abd al-Karim Soroush have tried to move ideological debates beyond factionalism toward serious engagement of the consequences of the success of the Islamic revolution.