The Rise of the Samurai and the Founding of the Kamakura Shogunate

As central authority weakened, professional warriors known as bushi, or samurai, emerged in the Japanese provinces from the ninth and tenth centuries onward, many descended from impoverished branches of the court aristocracy, including the Minamoto and Taira clans, secondary lines of the imperial family that had taken on clan surnames upon losing princely rank. The almost simultaneous rebellions of Taira no Masakado in eastern Japan and Fujiwara no Sumitomo in the Seto Inland Sea (935-941), during which Masakado went so far as to proclaim himself "new emperor" before being defeated and killed in 940, dramatically exposed the central government's real military weakness and reinforced the court's growing reliance on warrior clans to maintain order. From 1086 the system of insei, government by retired emperors, further deepened this dependence, since retired sovereigns relied on Minamoto and Taira warriors as their personal military force.