TheGyehae Treaty was signed in 1443 ("gyehae" is the Korean name of the year in thesexagenary cycle) between theJoseon dynasty andSō Sadamori as a means of controllingJapanese piracy and legitimizing trade betweenTsushima island and three Korean ports.^[1] It is also calledKakitsu Treaty (嘉吉条約,Kakitsu Jōyaku); 1443 is the third year of theKakitsu era in the Japanese calendar.

Tsushima was then an important trade center. The private trade started betweenGoryeo, Tsushima,Iki, and Kyūshū, but halted during theMongol invasions of Japan between 1274 and 1281. TheGoryeosa, a history of the Goryeo dynasty, mentions that in 1274, an army of Mongol troops that included many Korean soldiers killed a great number of Japanese on the islands.

Tsushima became one of the major bases of thewokou, Japanese pirates, also calledwakō, along with the Iki andMatsuura. Repeated pirate raids made the Goryeo dynasty and the subsequentJoseon dynasty at times placate the pirates by establishing trade agreements and negotiate with theMuromachi shogunate and its deputy in Kyūshū and at times use force to neutralize the pirates. In 1389, GeneralPak Wi (朴威) of Goryeo attempted to clear the island of Wokou pirates, but uprisings in Korea forced him to return home.

On June 19, 1419, the recently abdicated KingTaejong of Joseon sent GeneralYi Jongmu to an expedition to Tsushima Island to clear it of the Wokou pirates, using a fleet of 227 vessels and 17,000 soldiers, known in Japanese as theŌei Invasion. The Korean army returned to the Korean Peninsula on July 3, 1419,^[2] and Korea gave up occupation of Tsushima.^[3] In 1443, the Daimyo of Tsushima,Sō Sadamori 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.^[4]

This treaty was signed by Joseon dynasty kingSejong the Great and the Lord of Tsushima island in 1443. Thedaimyō 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 substantialstipend from the Korean government and aiding to stop any Japanese coastal pirate raids on Korean ports.^[5][6] The treaty was discarded by therevolt of the Sampo in 1510.

• List of treaties
• Ōei Invasion
• Byeon Hyo-mun

• Japan–Korea relations
• History of the foreign relations of Japan
• Treaties of Japan
• 1440s in Japan
• 1443 in Asia
• 15th century in Korea
• Treaties of Joseon

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