In 1609, the Shimazu clan, which controlled the region that is now Kagoshima Prefecture, invaded the Ryukyu Kingdom. The Ryukyu Kingdom was obliged to agree to form a suzerain-vassal relationship with the Satsuma and the Tokugawa shogunate, while maintaining its previous role within the Chinese tributary system; Ryukyuan sovereignty was maintained since complete annexation would have created a conflict with China. The Satsuma clan earned considerable profits from trade with China during a period in which foreign trade was heavily restricted by the shogunate.