By 1840, the Tokugawa family had maintained its political and economic supremacy over all of Japan for a little less than 250 years. The leader of this clan was the shogun (Jp. shōgun) or more formally the sei-i tai-shōgun, "supreme commander for the pacification of barbarians," who was declared to be the most powerful leader in Japan. Ruling from the largest city in the world, Edo (later renamed Tokyo in the Meiji period), the shogun demanded allegiance from the approximately 250-300 daimyō, to whom the shogun had offered lands throughout Japan. The system which had emerged in the 17th century became known as the bakuhan seido, or the system of rule between the central authority, bakufu, and the many domains, han, which the shogun had configured.
The Tokugawa family assumed this authority after defeating a formidable army of opposing clans at the battle of Sekigahara in 1600. The bakufu government thus formed and led by a Tokugawa shogun maintained legitimacy through his appointment to office by the weakened emperor who remained in Kyoto. The most powerful leader of each domain was called a daimyō, and he held that role through appointment by the shogun.
During the first century of shogun rule, political, economic, and social rules emerged which provided for the primacy of the bakufu over the han. This was ensured by the military superiority of the central authority at the Edo; by its large land holdings, heavily concentrated around Edo, but also spread throughout the rest of Honshū and Kyūshū and Shikoku; and by the political and social rules issued in its name which favored the shogun's power. Thus, for about one hundred years, the Tokugawa shoguns maintained tight control over the han. Japan's economy at this time was based on rice, and Tokugawa had by far the greatest area under rice cultivation. It also maintained the largest number of samurai, the military component of the system, and demanded and received allegiance from the 270 or so daimyō, and their samurai vassals, who lived in the established han. Through the mid-nineteenth century this system, though faltering significantly, continued to guarantee peace.
In its ideal form, the bakuhan system provided for central authority with power over the lives and livelihood of everyone residing in each han and the daimyō who was in charge. At the same time the daimyō had considerable power within his own lands as long as he did not break any of the rules sent down from Edo. In actuality, however, by 1840, this system had become only a shell of its former self, and much which remained on paper and was plastered on placards and declared in proclamations was no longer working in fact.
The bakuhan system, 17th century
When Tokugawa Ieyasu defeated his enemies in 1600 and began the dynasty which was to last for over 250 years, he claimed large land holdings for himself and his household, gave land holdings with prescribed borders called han to those daimyō who had fought for him. Daimyō who fought against him in the battle were given a han in more remote, provincial, and less strategic areas of Japan. In this way he began the system which was designed to ensure Tokugawa power as well as peace in the land. As time went on his successors added laws to this system, further guaranteeing their own authority.