What were the major motives for converting to islam when the umma opened up to non-muslims in the abbasid era?

- The status of non-Muslims was inferior. During the Umayyad Period it was specially the case, as Islam was Arab-centric and only  Muslim Arabs had access to high positions in the administration and bureaucracy. During the Abbasid Period, Caliphs decided to rely more and more on non-Arabs, notably Persians and in 930 CE a law was passed that made it mandatory for all bureaucrats of the Empire to be Muslims. Therefore non-Muslims had a professional incentive to further their career.

- The dhimmi status involved the payment of a "protection" tax that had to be paid by non-Muslims to Muslims. Poor people had no choice but to convert if they could not afford the payment of such tax.

- As the Empire prospered and developed many Muslims migrated to conquered lands that were majoritarily non-Muslim before their arrival. Their increased influx made the new majority relevant and non-Muslims preferred to convert in order to assimilate to their new reality.

b) the confederacy had to pay all union war expenses.