In addition to Korea (1392), Thailand (1409) and other Southeast Asian polities, the kingdom maintained trade relations with Japan (1403), and during this period a unique political and cultural identity emerged. However, in 1609 the Japanese feudal domain of Satsuma invaded the kingdom on behalf of the first "shōgun" Tokugawa Ieyasu and Tokugawa shogunate (1603–1867) because the Ryukyu king Shō Nei refused to submit to the shogunate. The kingdom was forced to send a tribute to Satsuma, but was allowed to retain and continue its independence and relations and trade with China (a unique privilege, as Japan was prohibited from trading with China at the time). This arrangement was known as a "dual vassalage" status, and continued until the mid-19th century.