The next period, after Muhammad dies, the leadership of the community, of the ummah, goes to the caliphs. And this actually becomes a contentious issue that we'll talk about in other videos. It's the seed of the eventual schism between the Sunnis and the Shias. But this next period, the Rashidun, or the rightly guided caliphs, caliph means successors, essentially successors to Muhammad. Under these four caliphs, you see Islam spread from as far west as Tunisia and Egypt all the way through Persia. And keep in mind, this is spreading, overtaking, conquering what used to be controlled by very powerful empires, the Byzantine Empire or Eastern Roman Empire, taking territory from them here, and then Sassanid Persia, taking territory from them, and this is less than 30 years. And then it spreads even more.