Sō clan
Being based on the mountainous island, the Sō clan heavily relied on trade with Korea. Fortunately, the Sō clan shared mutual interests with the Joseon Dynasty. In 1443, the Daimyō of Tsushima, proposed a Gyehae treaty. The number of trade ships from Tsushima to Korea was decided by this treaty, and the Sō clan monopolized the trade with Korea. The Sō were required to greatly reduce the number of pirate attacks on Korea, and in return would be granted a virtual monopoly on Japanese trade with their neighbors on the peninsula. This would later lead to the emergence of the Sō as one of the major clans in Japan, their wealth and power from trade more than making up for their small territory and submissive position vis-a-vis Korea.