The Kyehae Treaty was signed in 1443 ("Kyehae" is the Korean name of the year in the sexagenary cycle) between the Joseon and the SÃ Â clan head Sadamori as a means of controlling wokou and legitimizing trade between Tsushima and three Korean ports. It is also called ; 1443 is the third year of the Kakitsu era in the Japanese calendar. The treaty was the last document signed between Japan and Korea for 433 years till 1876.
Tsushima was then an important trade center. The private trade started between Goryeo, Tsushima, Iki, and Kyà «shà «, but halted during the Mongol invasions of Japan between 1274 and 1281. The Goryeosa, a history of Goryeo, reports that in 1274, a Mongol army that included many Korean soldiers killed many Japanese on the islands.
Tsushima became one of the major bases for the wokou, along with the Iki and Matsuura. Repeated pirate raids led Goryeo, and subsequently Joseon, to placate pirates by establishing trade agreements and negotiating with the Ashikaga shogunate and its deputy in Kyà «shà «, as well as using force to neutralize them. In 1389, General Pak Wi ( of Goryeo attempted to clear Tsushima of wokou, but uprisings in Korea forced him to return home.
On June 19, 1419, the recently abdicated King Taejong of Joseon sent General Yi Chongmu to an expedition to Tsushima to clear it of wokou, using a fleet of 227 vessels and 17,000 soldiers known in Japanese as the à Âei Invasion. The army returned to Korea on July 3, 1419, and Korea gave up occupation of Tsushima. In 1443, the Daimyo of Tsushima, proposed a Kyehae treaty. The number of ships permitted to trade between Tsushima and Korea was determined by this treaty, and the Sà  clan monopolized trade with Korea.
This treaty was signed by King Sejong the Great and the Lord of Tsushima island in 1443. The daimyà  of the So clan of Tsushima island was granted rights to conduct trade with Korea in fifty ships per year, in exchange for receiving a substantial stipend from the Korean government and aiding in stopping any wokou raids on Korean ports. The treaty was discarded by the revolt of the Sampo in 1510.