Okinawa was originally the heartland of the independent Ryukyu Kingdom with its capital at Shuri. While being a tributary state to China, Ryukyu found itself under a state of dual subordination after losing a war to Satsuma Domain of Japan. Satsuma directed Ryukyu to increase trade with China in order to circumnavigate the Tokugawa Shogunate's policy of enforced isolationism. Following multiple visits to Ryukyu by Europeans and the Meiji Restoration, Japan increased control over Ryukyu until 1879 when, following a number of incidents of Ryukyuan resistance or refusals, the kingdom was forcefully annexed. Okinawa then became an official prefecture. This was followed by a period of cultural assimilation in order to make the Ryukyuans Japanese.