Sankin kotai

Sankin-kōtai (参勤交代, "alternate attendance", a daimyō's alternate-year residence in Edo^?) was a policy of the Tokugawa shogunate during most of the Edo period of Japanese history. The purpose was to strengthen central control over the daimyōs (major feudal lords).

Toyotomi Hideyoshi had earlier established a similar practice of requiring his feudal lords to keep their wives and heirs at Osaka Castle or the nearby vicinity as hostages for loyal behavior. Following the Battle of Sekigahara and the establishment of the Tokugawa Shogunate, this practice was continued at the new capital of Edo as a matter of custom. It was made compulsory for the tozama daimyōs in 1635, and for the fudai daimyōs from 1642. Aside from an eight-year period under the rule of Tokugawa Yoshimune, the law remained in force until 1862.

The details changed throughout the 26 decades of Tokugawa rule, but generally, the requirement was that the daimyōs of every han move periodically between Edo and his fief, typically spending alternate years in each place. His wife and heir were required to remain in Edo as hostages while he was away. The expenditures necessary to maintain lavish residences in both places, and for the procession to and from Edo, placed financial strains on the daimyo, making them unable to wage war. The frequent travel of the daimyo encouraged road building and the construction of inns and facilities along the routes, generating economic activity.

There were a number of exceptions for certain fudai daimyōs in the vicinity of Edo, who were allowed to alternate their attendance in Edo every six months instead. Temporary exceptional dispensations were also occasionally granted due to illness or extreme extenuating circumstances.

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