The , also known as the Gihae Expedition (), was a 1419 invasion from Joseon against wokou (Japanese pirate) bases on Tsushima Island, which is located in the middle of the Tsushima Strait between the Korean Peninsula and Kyushu. The Japanese identifying phrase derives from the Ōei era (1394–1428), which is the Japanese era name of the calendar system in use in Japan. The corollary Korean identifying title derives from Gihae in the Chinese sexagenary cycle of the calendar system then in use in Joseon. In both, the terms are explicit equivalents for the Gregorian calendar year of 1419. Background From about 1400, despite its incorporation into the Japanese political order (this incorporation was however limited, to the point that Japanese authorities, regional and national, were unable throughout most of Japanese history to control and limit wokou activity originating in this area) before the Goryeo, Tsushima were located on the front lines that defended Japanese territory for much of its history. Historically, a large part of Tsushima's economy was sustained by trade with Korea; it was used as a "frontier territory" and a diplomatic meeting place between Korea and Japan, but was considered historically by Koreans as a vassal or dependent state of Korea, and despite a variety of changes in terminology over the ages designed to indicate its status as being in the Japanese sphere of influence, it was considered by many Koreans to be Korean land under foreign occupation. From the end of the Goryeo through the early Joseon, the coastal regions of Korea, their populations, and their resources were often the objective of wokou raids. In 1389, General Pak Wi () of Goryeo cleared the island of wokou, he burnt 300 ships and rescued more than 100 Korean captives. The Joseon ordered a strengthening of Korean naval defenses, a strategic response to the constant threat posed by the pirates. In 1396, Korean official Kim Sa-hyeong (김사형, 金士衡) led a campaign into Tsushima. Joseon subsequently asked the Ashikaga shogunate and its deputy in Kyūshū to suppress pirate activity, favoring legitimate traders. In exchange for certain privileges, it gave authority to Sō Sadashige, the de facto ruler of Tsushima Province, over ships sailing from Japan to Korea. When Sō Sadashige died in 1418, power was seized from Sadashige's infant son Sadamori (Tsutsukumaru) by Soda Saemontaro, a powerful wokou leader. Suffering from famine, wokou on Tsushima invaded Ming China in