MOHAMMAD

"For all their differences, the Byzantine and Sasanian Empires shared certain common features and faced similar challenges. Their rulers struggled to unify vast domains and fragmented populations by the use of force,when necessary , and by recourse to a religious ideology that they tried to impose on their subjects, which bolstered their claim to rule.Both,perhaps inadvertently , fostered movements with egalitarian tendencies that used religious ideas to blunt the harshness of existing social norms. Both faced the challenge of warding off external enemies on their frontiers ... Above all the two empires faced the challenge of each other . ... At stake was not merely Byzantine
versus Sasanian political control and economic influence, but also Christianity as opposed to Zoroastrianism and Hellenic as opposed to Iranian cultural traditions."(Muhammad and the Believers)