Throughout the twelfth century, two rival clans, the Minomoto and the Taira, struggled for supremacy in Imperial Japan. Each attempted a rebellion and, for a time, the Taira gained ascendancy. But their rule turned despotic and at last, during the Genpei War of 1179-1185, the Minomoto drove the Taira out of the capital and took control for themselves. At the final battle of Dan-no-ura, the Taira-born child-emperor and his family all jumped into the...