By the 12th century the ability of the emperor and his court to govern effectively had diminished. It was then that the samurai emerged as a distinct social class. They were held together by personal loyalty to powerful chiefs—the shoguns—who brought more territory under their control. Local wars among the chieftains continued for generations until finally, under the Tokugawa shogunate, the whole nation was united under one warlord. From the end of the 12th century until the Meiji Restoration, or resumption of the emperor's authority, in 1868, government was exclusively in the hands of the samurai class.

The behavior of the samurai was strictly regulated by a code of conduct called Bushido, which is translated as “way of the warrior.” The idea of the code developed in about the 13th century, and it encompassed the ideals of loyalty and sacrifice. By the 19th century it had become the basis of ethical training for the whole of Japanese society, and it contributed significantly to the tough Japanese nationalism and morale exhibited during World War II.

After the Meiji Restoration in 1868, the samurai class lost its privileged status. As a result, discontented samurai rose in rebellion during the 1870s, but the revolts were easily suppressed.