Brainstorming POD ideas and one idea that comes to head is this. Prior to the Battle of Qadisiyyah the Muslim Caliph offered to the Persian Emperor to convert to Islam. At this time the opinion of the Caliphs was less on expansionism and was somewhat reluctant to invade Persia as a whole.
The battle itself took place after a previous invasion of Iraq by the Arabs that ha kicked out the Persians until a counter-attack by the Persians and Byzantine preparations for their own offensive forces the Islamic Arabs out.
Also to give context this is also after the disaster of Yarmouk that had crushed the Byzantines. Yazdegerd was also at this point coming out of very recently gaining control over Persia following the strife of the Byzantine-Sassanid wars. The only thing that held the two forces allied together was a recognition of the Arab threat and a marriage of Heraclius' daughter to the Persian Emperor.
What could have happened if Yazdegerd had converted or just agreed to pay the Jaziyah tax as a form of ransom (like the Byzantines did to the Persians for sometime).
The battle itself took place after a previous invasion of Iraq by the Arabs that ha kicked out the Persians until a counter-attack by the Persians and Byzantine preparations for their own offensive forces the Islamic Arabs out.
Also to give context this is also after the disaster of Yarmouk that had crushed the Byzantines. Yazdegerd was also at this point coming out of very recently gaining control over Persia following the strife of the Byzantine-Sassanid wars. The only thing that held the two forces allied together was a recognition of the Arab threat and a marriage of Heraclius' daughter to the Persian Emperor.
What could have happened if Yazdegerd had converted or just agreed to pay the Jaziyah tax as a form of ransom (like the Byzantines did to the Persians for sometime).