Enter the Shoguns: Japan's austere, ruthless, but statesmanlike new ruler, Yoritomo Minamoto, set up his government in Kamakura (just south of modern Tokyo), well away from the "softening" influence of court life that had been the undoing of his predecessor, Kiyomori. First of the national rulers to take the title of sei-i tai-shogun ("barbarian-subduing great general"), Minamoto expanded and consolidated his power by confiscating lands from some of the defeated Taira and redistributing them to his samurai vassals. Minamoto died in 1199, and the feudal structure passed intact to the tutelage of his widow's family, the Hojo, who were content to play regent to a figurehead shogun, in much the same way as the Fujiwara had done with the emperor. The fiction of Japanese imperial power had become infinitely extendable. The emperor at Kyoto — still seconded by a Fujiwara regent at court — legitimized a Minamoto who was himself a military dictator controlled by a Hojo regent. In a country where form and substance were inextricably interrelated, two things counted in politics: symbolic authority and real power. Neither could exist without the other. A thwarted Mongol invasion in 1274 weakened the Kamakura regime. The fighting brought none of the usual spoils of war that provincial warlords and samurai had come to expect as payment. And the treasury was empty after earthquake, famine, and plague had crippled the economy. Buddhist monasteries were using their private armies to support imperial ambitions to bring power back to Kyoto. Worst of all, the Kamakura warriors, resenting the way the Kyoto court referred to them as "Eastern barbarians," sought refinement in a ruinous taste for luxury: extravagant feasts, rich costumes, and opulent homes. Kamakura was falling apart. 
How did the economy collapse?
Revolt of the Samurai vassals