The reign of the Umayyad dynasty began to unravel after the empire became overextended. By 717, the Umayyads were having trouble defending frontiers and preventing insurrections, and the financial situation of the empire had become untenable, despite attempts by the caliph ʿUmar II to stave off disintegration. Playing off broad discontent, the ʿAbbāsids spurred a successful rebellion that eventually upended the Umayyads in 750.