The initial years (126-145) of al-Mansur's reign presented several significant challenges to nascent Abbasid hegemony, and the resulting confrontations constitute the central focus of this section of Tabari's Tarikh. After Abu Jafar succeeded his brother Abu al-Abbas as caliph, the second of the Abbasid dynasty, he moved against his recalcitrant uncle, Abdallah b. Ali, and against the potential threat that he perceived in the person of the commander in Khurasan, Abu Muslim. Eliminating the latter and containing the former freed the caliph to address a series of other onslaughts and insurrections.