Taking advantage of widespread discontent with Ummayad rule, descendants of al-Abbas brought about the end of the Ummayad Caliphate in the East. The capital of the Caliphate moved to Baghdad, Iraq. Caliph Abu-al-Abbas and his descendants reigned from 750 to 1258, when Baghdad fell to the Mongols. From 945, they did not rule as such, but were "under the protection" of the Buwayhids, and later the Seljuks.- Category ID : 459925
Summary article of the family which formed the last Arab Caliphates; also covers their decline, until only symbolic value remained. From Encyclopaedia of the Orient
An online exhibition from the Metropolitan Museum of Art (New York) offers a profile of the caliphate, and illustrations of their cultural and artistic achievement.