After Welîd, the Omeyyad dynasty lasted six-and-thirty years. But it began to rest on a precarious basis. For now the agents of the house of Hâshim, descendants of the Prophet and of his uncle Abbâs, commenced to ply secretly, but with vigour and persistency, their task of canvass and intrigue in distant cities, and especially in the provinces of the East. [Sidenote: The Shîya faction canvass for Alyite pretenders.] For a long time, the endeavour of these agitators was directed to the advocacy of the _Shîya_ right; that is to say, it was based upon the Divine claim of Aly, and his descendants in the Prophet’s line, to the Imâmate or leadership over the empire of Islam.[604] Risings everywhere from time to time took place in favour of some one or other in whose veins flowed the blood of Aly. Everywhere the attempts were suppressed, the pretenders slain or cast into prison, and their armies defeated in the field. [Sidenote: Canvass in favour of house of Abbâs.]But a new and more fatal danger soon arose. The discomfiture of the Shîyas paved the way for the designing advocates of the other Hâshimite branch, namely, that of the house of Abbâs, the uncle of the Prophet. These had all along been plotting in the background, and watching their opportunity. They now vaunted the claims of this line, and were barefaced enough to urge that, being descended from the uncle of Mahomet through _male_ representatives, they took precedence over the direct descendants of the Prophet himself, because these came through Fâtima in the _female_ line. [Sidenote: Abul Abbâs supported by Abu Muslim in Persia. A.H. 130.]About the year 130 of the Hegira, Abul Abbâs, of Abbasside descent, was put forward in Persia, as the candidate of this party, and his claim was supported by the famous general Abu Muslim. Successful in the East, Abu Muslim turned his arms to the West. [Sidenote: Battle of the Zab. A.H. 132. A.D. 750.] A great battle, one of those which decide the fate of empires, was fought on the banks of the Zab; and, through the defection of certain Khârejite and Yemen levies, was lost by the Omeyyad army. Merwân II., the last of his dynasty, was driven to Egypt, and there killed in the church of Bussir, whither he had fled for refuge. [Sidenote: Abul Abbâs succeeds to the Caliphate.]At the close of the year 132,[605] the black flag, emblem of the Abbassides, floated over the battlements of Damascus. The Omeyyad dynasty, after ruling the vast Moslem empire for a century, now disappeared in cruelty and bloodshed. Alyite, Omeyyad, and Khârejite, were equally the victims of the exterminating sword of the first Abbasside Caliph, who thereby earned for himself the unenviable name of _Al Saffâh_, ‘The Bloody.’[606] [Sidenote: Omeyyad dynasty in Spain. A.H. 138. A.D. 756.]