In the late twelfth century, Japanese people called the transitional period in which they were living the "age of warriors." Feudal clans fought civil wars, and warriors from the Kanto Plain rose up to restore the military regime of their shogun, Yoritomo. The whole of this intermediary period came to represent a gap between two stable societies: the ancient period, dominated by the imperial court in Heian (today's Kyoto), and the modern period,...