Some of this is more fresh in my mind because I recently listened to a new episode of Revolutionary Left (RevLeft) Radio that gets into it: From Persia to Iran: Islam, Empire, and the Politics of West Asia. You might want to give a listen. The guest is Adnan Husain (“Professor of Medieval history and Chair of the Religious Studies department at Queens college”) who also hosted the Guerilla History podcast. Anyway, they talk quite a bit in good depth about the history of Islam. The stuff I mentioned in my other comment I already mostly knew about, but there was a lot more in this episode that I learned. They also discuss the relevance of this deep history with respect to the current war the Great Satan and the Entity are waging against Iran.