u/Grand-penetrator

So in this scenario the rise of Islam still happens, but instead of conquering all of Persia the Arabs only manage to take Arabia and Mesopotamia from the Sasanians, leaving them intact in Iran proper (similar to how the Byzantines lost Syria and Egypt but still survived).

The Arabs still successfully complete their other conquests in Africa and Iberia, completely changing the power dynamics, but Islam never got inside Persia so instead of 2 there are now 3 major religiously distinct players.

How would this affect the region and world history as a whole? How would a Zoroastrian Iran shape modern geopolitics, assuming the religion is still the majority in the region until this day?