'ABBASID DYNASTY

second of the two great dynasties of the Muslim Empire of the Caliphate. It overthrew the Umayyad caliphate in AD 750 and reigned as the 'Abbasid caliphate until destroyed by the Mongol invasion in 1258. The name is derived from that of the uncle of the Prophet Muhammad, al-'Abbas (died c. 653), of the Hashimite clan of the Quraysh tribe in Mecca. From c. 718, members of his family worked to gain control of the empire, and by skillful propaganda won much support, especially from Shi'i Arabs and Persians in Khorasan. Open revolt in 747, under the leadership of Abu Muslim, led to the defeat of Marwan II, the last Umayyad caliph, at the Battle of the Great Zab River (750) in Mesopotamia and to the proclamation of the first 'Abbasid caliph, Abu al-'Abbas as-Saffah. Under the 'Abbasids the caliphate entered a new phase. Instead of focussing, as the Umayyads had done, on the West-on North Africa, the Mediterranean, and southern Europe-the caliphate now turned eastward. The capital was moved to the new city of Baghdad, and events in Persia and Transoxania were closely watched. For the first time the caliphate was not coterminous with Islam; in Egypt, North Africa, Spain, and elsewhere, local dynasties claimed caliphal status. With the rise of the 'Abbasids the base for influence in the empire became international, emphasizing membership in the community of believers rather than Arab nationality. Since much support for the 'Abbasids came from Persian converts, it was natural for the 'Abbasids to take over much of the Persian (Sasanian) tradition of government. Support by pious Muslims likewise led the 'Abbasids to acknowledge publicly the embryonic Islamic law and to profess to base their rule on the religion of Islam. Between 750 and 833 the 'Abbasids raised the prestige and power of the empire, promoting commerce, industry, arts, and science, particularly during the reigns of al-Mansur, Harun ar-Rashid, and al-Ma'mun. Their temporal power, however, began to decline when al-Mu'tasim introduced non-Muslim Berber, Slav, and especially Turkish mercenary forces into his personal army. Although these troops were converted to Islam, the base of imperial unity through religion was gone, and some of the new army officers quickly learned to control the caliphate through assassination of any caliph who would not accede to their demands. The power of the army officers had already weakened through internal rivalries when the Iranian Buyids entered Baghdad in 945, demanding of al-Mustakfi (944-946) that they be recognized as the sole rulers of the territory they controlled. This event initiated a century-long period in which much of the empire was ruled by local secular dynasties. In 1055 the 'Abbasids were overpowered by the Seljuqs, who took what temporal power may have been left to the caliph but respected his position as religious leader, restoring the authority of the caliphate, especially during the reigns of al-Mustarshid (1118-35), al-Muqtafi, and an-Nasir. Soon after, in 1258, the dynasty fell during a Mongol siege of Baghdad.