It was in the context of a West Asian world dominated by the Sasanians that Islam began as a political and religious movement in Arabia Deserta. The Sasanian regime, however, was extending itself too far. The cost of the war with Byzantium was mounting, and the task of managing all the new territories was something for which their administration was not ready. The Sasanian government was in fact unable to control its own empire: the domain had simply outgrown the administration...

The conventional narrative of the conquest of Iran, based mainly on accounts drawn from standard Islamic histories such as those of al-Balādhurī, al-Ṭabarī, and so forth, considers this event to have been the result of quick and successful campaigns by Muslim armies. These campaigns, exemplified by the battles of Qādisiyya and Nahāvand, are understood to have caused the near-instantaneous fall of the Sasanians as an imperial and cultural unit. Furthermore, this fall is assumed to be the fall of Iran itself; as a result, it represents no less than a national failure, the beginning of Iran’s subordination to Arabia and/or Islam...

Islam was born out of the imperial struggles of Late Antiquity, a period during which claims of political authority were commonly intertwined with assertions of religious truth. Islam was unusual in this period in that it recognized the partial authenticity of the Jewish and Christian messages while asserting its superiority as the final revelation to humanity, as well as establishing a world empire aiming to restore God's rule on earth...