The result of defeat of rival prophets, known as the Ridda Wars, brought the return of the Arabian tribes to Islamic fold. Arab warriors were driven by a new sense of common cause and strength. They were drawn to the campaigns of expansion by the promise of a share in the treasure to be won on rich farmlands. Bedouin tribes of Arab descent did not want to have mass conversions to Islam because people would convert voluntarily. People would convert because if one is Islam they were exempt from lucrative taxes levied on Christians.
In dominance over the Fertile Crescent, the Sasanian Empire of Persia was more vulnerable. The aristocratic class exploited the farmers, who made up most of the population. The Sasanian Empire set out against the Arab invaders with poorly prepared forces, were forced to retreat eastward. The capitol was then taken, armies destroyed, generals and rulers were slain, and Muslims prevailed and destroyed the empire. The Byzantine Empire was a stronger adversary with their ability to resist the Muslim onslaught by the defection of their own frontier Arabs and support from Christians of Syria and Egypt. Christian’s sects dominated and resented the rule of the Orthodox Byzantines, who they taxed heavily and openly prosecuted. The Muslims would not only tolerate the Christians but taxed the less heavily than the Byzantine Empire did, therefore the Christian groups rallied with the Arabs. The Empire was reeled from the Arab assaults because of long wars fought with Persia in the Decades before. Syria, western Iraq, and Palestine were taken quickly and probes were made in Egypt by the invaders. The