how did the tokugawa shoguns kept control of daimyo during the period of their rule
Tokugawa shogunate The emperor, nominally a religious leader, held no real power; this was invested in the shōgun. The shogunate had the power to discard, annex, and transform domains. The sankin-kōtai system of alternative residence required each daimyō to reside in alternate years between the han and the court in Edo. During their absences from Edo, it was also required that they leave family as hostages until their return. The huge expenditure sankin-kōtai imposed on each han helped centralize aristocratic alliances and ensured loyalty to the shōgun as each representative doubled as a potential hostage.
Convention of Kanagawa The final article, Article Twelve, stipulated that the terms of the treaty were to be ratified by the President of the United States and the "August Sovereign of Japan" within 18 months. At the time, shōgun Tokugawa Iesada was the de facto ruler of Japan; for the Emperor to interact in any way with foreigners was out of the question. Perry concluded the treaty with representatives of the shogun, led by plenipotentiary Hayashi Akira (林韑) and the text was endorsed subsequently, albeit reluctantly, by Emperor Kōmei.[10] The treaty was ratified on 21 February 1855.[11]