The Mongols are an example of people who are fragmented initially, tribal, unified by Genghis Khan, and through that unification, were able to spread incredibly rapidly and take on some long, historic, and possibly declining empires. So I'll leave you there. It's a fascinating question that historians debate to this day. Islam started awfully fast and spread awfully fast. Why did this happen? Was it some unique characteristics of Muhammad? Was it some unique characteristics of the religion?