The bakuhan taisei was the feudal political system in the Edo period of Japan. Baku, or "tent," is an abbreviation of bakufu, meaning "military government" — that is, the shogunate. The han were the domains headed by daimyo.
Vassals held inherited lands and provided military service and homage to their lords. The Bakuhan Taisei split feudal power between the shogunate in Edo and provincial domains throughout Japan. Provinces had a degree of sovereignty and were allowed an independent administration of the Han in exchange for loyalty to the Shogun, who was responsible for foreign relations and national security. The shogun and lords were all daimyo: feudal lords with their own bureaucracies, policies, and territories. The Shogun also administered the most powerful han, the hereditary fief of the House of Tokugawa. Each level of government administered its own system of taxation.
The Shogun had the military power of Japan and was more powerful than the emperor, who was a religious and political leader.
The shogunate had the power to discard, annex and transform domains. The sankin koutai system of alternative residence required each daimyo would reside in alternate years between the han and attendance in Edo. In their absence from Edo it was also required that they leave family as hostages until their return. The huge expenditure sankin-kotai imposed on each han helped centralize aristocratic alliances and ensured loyalty to the Shogun as each representative doubled as a potential hostage.
Tokugawa's descendants further ensured loyalty by maintaining a dogmatic insistence on loyalty to the Shogun. Fudai daimyo were hereditary vassals of Ieyasu, as well as of his descendants. Tozama, or "outsiders", became vassals of Ieyasu after the battle of Sekigahara. Shinpan, or "relatives", were collaterals of Tokugawa Hidetada. Early in the Edo period, the shogunate viewed the tozama as the least likely to be loyal; over time, strategic marriages and the entrenchment of the system made the tozama less likely to rebel. In the end, it was the great tozama of Satsuma, Choushuu and Tosa and to a lesser extent Hizen that brought down the shogunate. These four states are called the Four Western Clans or Satchotohi for short.
The number of han (roughly 250) fluctuated throughout the Edo period. They were ranked by size, which was measured as the number of koku that the domain produced each year. One koku was the amount of rice necessary to feed one adult male for one year. The minimum number for a daimyo was ten thousand koku; the largest, apart from the shogun, was a million.