The expenses of enforcing Umayyad rule in Iraq and the expansionist war efforts along multiple fronts, including the enormous cost of the failed sieges of Constantinople in 717–718, had erased much of the monetary gains from the conquests of Transoxiana, Sind and the Iberian Peninsula under al-Walid I and caused a financial crisis in the Caliphate. Among the solutions of Yazid's predecessor to the fiscal burden were the withdrawal of the Syrians from Iraq, a halt on conquests and near elimination of grants to Umayyad princes, as well as an unrealized goal to withdraw Arab troops altogether from Transoxiana, the Iberian Peninsula and Cilicia. The most significant reforms of Umar II granted equality to the "mawālī" in Khurasan, Sind, Ifriqiya and the Iberian Peninsula by abolishing the "jizya", the poll tax traditionally exacted on non-Muslim subjects but in practice extended to non-Arab Muslim converts, and instituting equal pay for "mawālī" in the ranks of the Caliphate's Arab-dominated armies. According to Blankinship, the reforms favoring the "mawālī" may have been guided by Umar II's piety, but also a fiscal consideration: if equal treatment with the Arabs made the government popular with the "mawālī" it could translate into delegating an increased security role for the "mawālī" in their native provinces and their enthusiastic defense of the Caliphate's frontiers, thereby reducing the expense of deploying and garrisoning Arab troops.