Both the Persian and East Roman empires…
628 CE to 639 CE
Both the Persian and East Roman empires have already demobilized, their human and material resources exhausted, and both have ceased to support those client states on the frontiers of the Arabian Peninsula that had restrained the Bedouin of the desert for the past century.
Consequently, they are vulnerable to the sudden emergence of the Islamic Rashidun Caliphate, whose forces invade both empires only a few years after the war.
The Muslim Arabs have overrun Mesopotamia and brought much of central Persia under their control by the end of 639.
Most of the lands of the Persian Empire, including Bactria, the Caucasus, and Makran, are annexed to the Rashidun Caliphate, the first Islamic state.
The Caliphate now begins the conquest of Egypt.