The Abbasid Caliphate replaced the Umayyad dynasty as the ruling house of the Islamic empire in 750 through a six-year insurrection mounted in Khurasan (the north-eastern Iranian frontier of the Umayyad state) by a coalition of grievances that the Umayyad administration had accumulated across nearly a century of rule: the Arab tribal factionalism that the Umayyads had been unable to settle; the dissatisfaction of the non-Arab Muslim converts (the mawali) at their fiscal and legal subordination to the Arab establishment; the Shia partisans of the family of Ali, who had never reconciled themselves to Umayyad rule and who provided a continuing source of religious-political opposition; and the wider Persian cultural and administrative tradition that the Umayyads had never wholly absorbed. The new dynasty took its name and its dynastic legitimacy from descent from al-Abbas, the uncle of the Prophet Muhammad — a more distantly related line than the Alids, but one that gave the Abbasids a claim to the religious authority that had been the principal Umayyad weakness.
The Umayyad crisis
The Umayyad caliphate established by Mu'awiya in 661 had presided over the first century of the Islamic empire's expansion — from Iberia to the Indus, with capital at Damascus and an Arab-aristocratic political system in which the Arabian tribal nobility administered an empire whose Coptic, Aramaic, Persian and Berber populations were taxed differently from the Arab Muslim elite. The system had been workable while the empire was expanding and while the Arab tribes accepted the Umayyad leadership; by the 740s it was workable in neither sense. The military expansion had substantively stalled after the 732 setback at Poitiers in Gaul and the 740 reverses on the Byzantine and Khazar frontiers; the Arab tribal factions (the Qays and the Yaman) had become the principal lines of political division within the empire, with the Umayyads progressively unable to manage the balance between them.
The political-religious case against the Umayyads was, by the 740s, fully developed. The dynasty's secular character — the late-Umayyad caliphs had built palace cities and conducted what the religious specialists regarded as a court culture inconsistent with the egalitarian-prophetic origins of Islam — alienated the religious establishment. The third Civil War of 744–47, opened by the assassination of al-Walid II and prosecuted across the empire between competing Umayyad claimants, broke the dynasty's political coherence. The succession of al-Walid II, Yazid III, Ibrahim and Marwan II within three years produced the political opening that the Hashimite movement had been waiting two decades to exploit.
The Hashimite organisation
The Hashimite movement — named for the Banu Hashim, the larger Quraysh clan to which both the Alid and Abbasid lines belonged — had been operating as an underground political-religious network in Khurasan and Iraq from the 720s. The principal organisers were Iraqi Shia agents who had been dispatched to Khurasan by the Imami leadership, and who there established themselves among the Arab tribal populations and the converted Persian client population. The movement's slogan was al-rida min al Muhammad — "the chosen one from the family of Muhammad" — with deliberate ambiguity about which branch of the family was meant. The Abbasid claim to the leadership was held in reserve, to be asserted only when the Umayyad state had been fully broken.
The conversion of the movement into open insurrection was effected by Abu Muslim al-Khurasani — a young agent of obscure origins, possibly Persian, possibly Arab, who had been dispatched to Khurasan in 745 by the Abbasid leader Ibrahim ibn Muhammad with full authority to raise the revolt. Abu Muslim raised the black banners — the Hashimite colours — at Sefidanj near Merv on the 9th of June 747, and within a year had occupied Merv and the principal Khurasan towns. The Umayyad governor of Khurasan, Nasr ibn Sayyar, fled west; the Khurasan provincial army defected to the rebellion in stages.
The Great Zab
The decisive engagement was the battle of the Great Zab on the 25th of January 750 — fought along the lower Zab river east of the upper Tigris, between the rebel army under the new Abbasid commander Abdullah ibn Ali (uncle of the eventual caliph al-Saffah) and the Umayyad caliph Marwan II in person, leading the remnants of the Syrian field army. The rebel force was approximately 12,000 men, with the cohesion produced by three years of successful campaigning; the Umayyad force was approximately 12,000 to 15,000, drawn from a Syrian army that had been fighting itself for the previous half-decade. The battle was decided by a rebel night march that turned the Umayyad flank, followed by a frontal assault at dawn that broke the centre. Marwan fled west toward Egypt and was killed near Fayyum in August 750, the last Umayyad caliph.
The new caliph, Abdullah ibn Muhammad al-Saffah ("the shedder of blood", a designation that became a cognomen rather than a proper name), had been proclaimed at Kufa in November 749 and confirmed by the post-Zab military and religious deliberation. The early Abbasid administration was conducted from al-Hira and the lower Iraqi cities for the first decade, while the question of the dynastic capital was settled.
The purges
The consolidation of the new dynasty required the elimination of two potential threats. The first was the surviving Umayyad family. The principal massacre took place at a banquet held by Abdullah ibn Ali for Umayyad notables at Jaffa in June 750, at which approximately eighty members of the family were killed. The few survivors who escaped to Iberia under Abd al-Rahman I would found the independent Umayyad emirate of Cordoba — and a century and a half later, the independent caliphate that constitutes Volume X of this library.
The second threat was the Shia partisans who had assisted the revolution but whose own claim to the caliphate (through the Alid line) had been displaced by the Abbasid succession. The Abbasid leadership prosecuted no immediate persecution of the Shia community but moved progressively, over the following decade, to detach the religious authority that the early movement had implicitly conceded to the Imami line. The Shia revolts of the 760s and after — particularly the Zaydi rising of 762 — were suppressed by the Abbasid military with the same dispatch as the earlier Umayyad operations against Shia movements.
The third threat was Abu Muslim himself, whose Khurasan reputation and military command made him a potential alternative to the new caliphal line. Abu Muslim was summoned to the second caliph al-Mansur's camp in 755 and murdered there on al-Mansur's order — an act for which the dynasty took political responsibility but whose theological awkwardness (Abu Muslim was the principal agent of the revolution that had legitimated the dynasty) required a generation of subsequent apologetic literature to manage.
By 754, when al-Mansur succeeded the short-reigned al-Saffah, the Abbasid succession was secure. The administrative and capital arrangements that al-Mansur would put in place over the following twenty years — and particularly the foundation of Baghdad — are the subject of the next chapter.
End of Chapter I