The Byzantines are a Christian empire, and the Sassanids are Zoroastrian. And Muhammad is from the Quraysh tribe, which is in charge of Mecca, which is considered a pilgrimage site for the various tribes of Arabia. But you can see that Arabia is fragmented, and this doesn't even do justice to how fragmented it was. But if you fast forward 200 years, you see a major change. And in fact, you wouldn't even have to go all the way to 800, even by the early eighth century, you see that Islam has spread from the Iberian Peninsula all the way to the Indus. And most of this, as mentioned, happens within 100 years after Muhammad's death. But let's ask our central question.