The office of caliph was regarded by Sunnis as successor to the Prophet Mohammed in his capacity as leader of the community.
The first four caliphs ruled from Medina; they were succeeded first by the Omayyads ruling from Damascus (661-750); then by the Abbasids of Baghdad, whose dynasty continued until 1258, although effective power was held by various dynasties of sultans, like the Buwayhids, and Seljuks.
In the 10th century two other dynasties took the title of caliph: a branch of the Omayyads in Spain, and the Fatimids in Cairo. The last Abbasid caliph was killed by the Mongol conquerors of Baghdad in 1258, and the caliphate came to an end.
The title was revived by the Ottoman sultan in the 19th century, but abolished by the Turkish Republican government in 1924.
Sunni / Shia Split