- Japanese: 宗家 (Sou-ke)
The Sô clan, based on Tsushima since the Kamakura period, were the traditional intermediaries in Japan-Korea relations. A tozama clan under the Tokugawa shogunate with an official kokudaka of 100,000 koku, they were also vassals of the Korean king, to whom they sent regular tribute missions, receiving 8,300 koku each year from the mid-17th century onwards, along with various Korean and Chinese goods, in exchange for tribute or gifts of Japanese and imported Southeast Asian goods.
Their relationship with the royal court of Joseon Dynasty Korea dates back to 1443. Joseon had already entered into various arrangements with other samurai clans, including the Ôuchi, offering opportunities for engaging in officially authorized trade in exchange for the samurai taking action against the wakô pirates harassing Korean shores. In 1443, Joseon entered into one such arrangement with the Sô, offering them authorization to send fifty trading ships to Korea each year and to levy certain maritime fees and cargo taxes, as well as an annual stipend of 200 koku of rice. In exchange, the Sô were to take a lead role in ensuring that all Japanese trading ships traveling to Korea were properly authorized, and in dealing with those which were not (namely, the wakô).
Proving themselves effective in policing the waters around their domain, and in otherwise managing Korean-Japanese interactions, the Sô quickly found they had made themselves indispensable enough that both Korean and Japanese (shogunate) authorities had difficulty removing them from this unique and privileged position. An incident in 1510, in which Sô clan ships aided Japanese fishermen and traders in attacking Korean ships as part of protests for concessions from Korean officials, was to be only the first of many in which Sô actions frustrated or directly opposed either Korean or Japanese authorities, but which ended in the Sô retaining their monopoly on Korean-Japanese relations. The number of ships to be sent to Korea every year was reduced as a result, however, from fifty to twenty-five, and Tsushima officials and representatives, previously free to some extent in their movement around Pusan or beyond, were now restricted to the Waegwan, or "Japan House," in Pusan. Another serious incident, known as the Yanagawa Affair, took place in 1634-1635, when the shogunate discovered that the Yanagawa clan, the top retainers to the Sô, had forged diplomatic documents several decades earlier; though it was clear that the Sô were complicit in drafting these documents which purported to speak on behalf of the shogunate without any shogunate approval, only the Yanagawa were punished, because of the importance of the Sô for maintaining trade and diplomatic relations with Korea. Monks were Kyoto were appointed, however, from then on to reside in Tsushima in a rotation, overseeing diplomatic correspondence.
After playing a role in Toyotomi Hideyoshi's Korean Invasions in the 1590s, Sô Yoshitoshi, reaffirmed as Lord of Tsushima han by the Tokugawa shogunate, worked to restore relations with Korea, and eventually succeeded. In 1607, the Joseon Court entered into relations with the shogunate, with the Sô clan as intermediaries. The Sô would retain their unique position throughout the Edo period, entrusted by the shogunate and by the Korean court with being the sole Japanese authorities engaging in trade and diplomatic relations with Korea. Tsushima officials regularly traveled to Pusan, some of the only Japanese to travel between Japan and the outside world in this period, and between 1607 and 1811, twelve official Korean embassies visited Japan, most traveling to Edo for an audience with the shogun. Though only holding an official kokudaka of 100,000 koku, the importance of the Sô clan / Tsushima han in maintaining relations with Korea was of great significance for Edo period Japan. The Sô clan was also given a special status in the sankin kôtai system, traveling to Edo only once every three years, instead of every other year.
- "Sô-ke" 宗家. Edo daimyô hyakka 江戸大名百家. Bessatsu Taiyô 別冊太陽. Spring 1978. p28.
- Robert Hellyer, Defining Engagement, Harvard University Press (2009), 31.
- Hellyer, 44.
- Ina Toshisada 伊奈利定, "Tôkaidô Futagawa juku honjin ni okeru daimyô-ke no riyô" 東海道二川宿本陣における大名家の利用, Honjin ni tomatta daimyô tachi 本陣に泊まった大名たち, Toyohashi, Aichi: Futagawa-juku honjin shiryôkan (1996), 55.