The successors to Mohammed as leaders of the Muslim religion bore the title of "Caliph." The Caliphate has undergone numerous historical transformations and was never recognized by the Shiites, who claim that the legitimate line was cut short by illegitimate usurpers. After the Mongols captured Baghdad in the thirteenth century, the Caliphate moved to Cairo. When Egypt was conquered by the Turks in the sixteenth century, the Ottoman sultans adopted the title and assumed the leadership of Sunni Islam, at least in the Arab world, to accompany their political dominance.
In 1923, under the leadership of Kemal Ataturk, the Turkish National Assembly abolished the Caliphate and exiled the last caliph and his family. Since then, Sunni Islam has been leaderless. At present, any prominent cleric can issue an authoritative ruling ("fatwa"), which, if unchallenged by others of equal stature, becomes part of religious or "Sharia" law. In the absence of a caliph, the religious authorities of al-Azhar University in Cairo and its ruling sheik have achieved a degree of acceptance as the final word on religious subjects.