the buckling frontiers of the empire. As the defeats also increased the bitterness and reluctance of the local frontier armies to campaign, the caliphs were left with little choice but send out detachments of the trusted Syrian army to the threatened fronts. This move proved doubly destabilizing for the Umayyad regime: the introduction of the Syrians in the frontier provinces further alienated the local troops, who saw their hitherto privileged position being threatened by the regime's favourites; while the parcelling out of the Syrian army to distant areas, and the losses it suffered, weakened the dynasty's main power base. This would be the major factor in the fall of the Umayyad Caliphate during the civil wars of the 740s and the subsequent Abbasid Revolution, which began in Khurasan. Notes References Sources Defile 731 Defile Defile Defile 730s in the Umayyad Caliphate