Abū al-ʿAbbās served as the first ʿAbbāsid Amīr al-Muʾminīn for a little over four years 749–54/132–6; a period that seems to have been only a prelude to the coming to power of his older and stronger brother Abū Jaʿfar. Indeed the figure of the latter loomed large behind that of the man who was supposed to be actually in power. Although other members of the ʿAbbāsid family were engaged in various important functions, Abū Jaʿfar seems always to have been at the centre of things at the crucial moment. This is not to say that he was running the affairs of the empire in his brother's name, for the latter did not have this power. From the moment of his elevation to this high office the real authority remained in the hands of the military leaders of the Revolution. In fact, his selection as the new Amīr al-Muʾminīn and the imposition of this choice on the political leadership was the first manifestation of the usurpation of power by the military. Abū Salama, the wazīr āl Muhammad and virtually the head of the provisional government, had not been challenged when he assumed the direction of affairs in Kūfa after the arrival of the revolutionary army there. Nevertheless, his vacillation and wavering for many weeks on the important question of installing a new Amīr al-Muʾminīn was a curious political mistake.