 Complete the following phrase:  The situation where conversion to Islam was penalized in an Islamic state could not last, and the devout Umayyad caliph Umar II 717720 has been credited with changing the taxation system. Modern historians doubt this account, although details of the transition to the system of taxation elaborated by Abbasid-era jurists are still unclear. Umar II ordered governors to cease collection of taxes from Muslim converts, but his successors obstructed this policy and some governors sought to stem the tide of conversions by introducing additional requirements such as circumcision and the ability to recite passages from the Quran. Taxation-related grievances of non-Arab Muslims contributed to the opposition movements which resulted in the 