On the Fact that Prior to the Muslim Conquests, North Africa and the Levant Were Largely Christian, Jewish, and Pagan, Persia Was Almost Exclusively Zoroastrian, and the Indian Subcontinent Had Strongly Embraced Hinduism

 And so what happened to all these people? Three possibilities. They were either a) annihilated en masse, b) compelled to pay the Jizya, or c) converted over to Islam as it was safer than the other two. Of course the truly compelling question remains. What will the useful idiots of today choose?