INTRODUCTION
During the Nara Period (710-794), an ineffective central government failed to suppress the growing power and autonomy of landed aristocrats, especially the Fujiwara clan. The nobles, who refused to pay taxes, grew wealthier, while the poorly-funded government lost most of its influence. By the Heian (794-1185), the Japanese emperor was merely the nominal head of the country, with the great landlords, or daimyo, assembling large personal armies to fulfill their military interests (e.g wars with and defense against rivals). These consisted of warriors called samurai (meaning "those who serve"), who lived by a code of honor called Bushido ("the warrior's way"), which stressed loyalty to one's lord, courage, and a fearless attitude toward death. As Japan's military class, they fought in all conflicts-from the wars with Mongol invaders from Yuan China to the Battle of Sekigahara, a decisive battle that made Tokugawa Ieyasu the shogun, or military ruler, of all Japan. After the centralized Tokugawa military government was implemented, however, the traditional war-centered lifestyle of samurai changed forever.
http://www.pbs.org/empires/japan/enteredo.html