After peaking around 1 BCE/CE, social development fell in both East and West. This was collapse on a whole new scale. Not only was it broader than ever before, affecting both ends of Eurasia, but it was also longer and deeper. Century after century it dragged on, cutting more than 10 percent off the East’s development score by 400 CE and 20 percent off the West’s by 500. How this happened, ushering in the end of the West’s fourteen-thousand-year-long lead in social development, is this chapter’s subject.
