Sō

The So were the lords of Tsushima Island, most likely an offshoot of the Koremune family of Dazaifu officials, although their genealogy claimed descent from the Taira. In 1246 Sō Shigehisa crushed the Abiru clan and received the stewardship; in the first Mongol invasion of 1274 Sukekuni died fighting at Sasuura.

As deputies of the Shoni, the So extended their hold during the Nanboku-cho wars and moved their seat to Tsushima around 1408. They secured the hereditary shugo post and broke with the Shoni in the 1440s.

Tsushima produced little rice, so the clan relied on trade and diplomacy with Joseon Korea. They endured the Oei invasion of 1419 and the Three Ports riots of 1510; though they joined the Western Army at Sekigahara in 1600, Tokugawa Ieyasu spared them for their Korean connections. After the 1609 Kiyu agreement they monopolised shogunal diplomacy with Joseon.