Goryeo made its first effort to establish diplomatic ties with Japan in 937, a year after King Taejo (the posthumous title of Wang Geon, founder of the Goryeo Dynasty) unified the Later Three Kingdoms. According to Japanese records, the king’s subordinates convened to discuss how to respond to the diplomatic letter from Goryeo. Two years later, in 939, Goryeo again dispatched a mission to Japan. It is not known why Goryeo sent this mission or how the Japanese kingdom reacted, but it was obvious that Goryeo was proactive in establishing relations with Japan. Then, in the 9th lunar month of 972 (the 23rd year of King Gwangjong’s reign), the Japanese central government received a message from the Dazaifu, the Kyushu public office that also oversaw the nation’s foreign affairs, to the effect that an official mission from the district of Namwon, Goryeo, had arrived at Tsushima Island. And in the 10th lunar month of the same year, the Dazaifu again reported the arrival of a mission from the district of Gimhae to Tsushima. Trade was the main goal of these local official visits to Japan.

Japan reacted negatively to such contacts with central and local officials from Goryeo. Diplomatic relations between Japan and Silla, Goryeo’s preceding dynasty, had been severed since the late 8th century. Moreover, pirates from Silla had often invaded Japan’s coasts during the chaotic times leading up to the dynasty’s fall. This gave Japan ample reason not to be friendly to the newly founded Goryeo dynasty. It is likely that the Japanese government permitted trade in the private sector but was reluctant to establish diplomatic ties with Goryeo.

Private trade continued to flourish, it seemed, as seen in the many records describing the arrival of Goryeo people on Japanese shores.

No official diplomatic ties were established between the two countries’ central governments, but from the mid-11th century, a two-way exchange continued to thrive in the border regions. A trade route connected Japan’s northern Kyushu and Goryeo’s Geumju (present-day Gimhae). In addition to the merchants, there were many who called themselves “ambassadors” during their visits to Goyreo – such as ambassador of Japan, of Tsushima, or Satsuma. These Japanese ambassadors offered local products and specialties to Goryeo, suggesting a tributary relationship. Because an increasing number of local officials and merchants from Kyushu began to present their native products to Goryeo from the late 11th century onwards, the practice was even described during the reign of King Munjong as “the Japanese crossing the sea from the east and offering precious treasures.”

Under such circumstances, it is interesting to note that Goryeo once made a request to Japan that they send doctors. In 1079 (the 33rd year of King Munjong’s reign), a document was sent by Yebin-seong, Goryeo’s agency for hospitality and protocol, requesting doctors to treat the king’s palsy. The document was delivered by a Chinese merchant by the name of Wang Chikjeong, who resided at the Dazaifu. The document read, “Since the king has been suffering from palsy for years, we ask your government to select the best doctors and send them to our country. If the chosen doctor’s treatment is effective, we shall offer generous rewards. Meanwhile, we are sending silk and musk as a token of our faith.”

Upon receiving the request, the Japanese government convened a series of intense meetings and reached a consensus that they would send doctors. However, at a meeting held several days later, a high-ranking official pointed out that it would bring shame to Japan if the king’s illness did not improve and the others agreed. To justify their refusal, the Japanese government found fault with the document: They claimed that in the letter, Goryeo had addressed Japan as if it were a powerful country like China, thus a good opportunity to establish friendly relations between the two countries was lost.

The above demonstrates how the two countries viewed each other. Both countries tried to occupy a superior position vis-a-vis the other. There had been frictions between Silla and Japan over diplomatic protocol, and the same situation repeated itself between Goryeo and Japan. The relationship between the two countries can be summarized as binary: they competed with each other on the central level, but at the same time, private trade and exchange thrived at a local level.

Local officials and private merchants from Japan would present, as tribute, native Japanese products to Goryeo. As this practice established itself over generations, it became a unique ceremonial ritual of tribute called “jinbong” (tributary trade).

From the end of the 12th century through the 13th century, Goryeo and Japan maintained these tributary trade relations, which was an official international exchange. Tsushima Island played a central role in tributary trade. Since mountains covered most parts of Tsushima, leaving little land for agriculture, the island had to engage in tributary trade for economic reasons. According to Goryeosa (History of Goryeo), the number of ships reserved for tributary trade was limited to two vessels a year and diplomatic papers as well as lists of goods had to be submitted. In the tributary trade relations, particularly notable was that when Tsushima sent tributes, Goryeo granted far more gifts than the received amounts. This means that Goryeo was generous in offering economic benefits to Tsushima Island. In 1185, Chikamitsu, the provincial governor of Tsushima, fled to Goryeo amid the civil war and became the subject of the Goryeo king, which might be explained by the friendly connection between Goryeo and Tsushima based on their tributary trade. It was in the spirit of the aforementioned friendship that the king of Goryeo sent many valuable gifts to Chikamitsu upon his return to Japan as acknowledgment of their relationship.

The Commandery of Southeastern Coast, the only administrative body that oversaw Korea-Japan affairs, was in charge of tributary trade. The office would at times follow orders given by the central government on cases that were outside its realm of authority, but in general dealt with most affairs independently. For Japan, Tsushima Island was the major player in the tributary trade but was under the control and supervision of the Dazaifu which assumed responsibility for handling foreign affairs for the shogunate government.

What was the historical background of this tributary trade relationship? The family of Taira no Kiyomori, who had seized power across Japan, strongly promoted trade with Southern Song of China. Previously, Japan had refused Goryeo’s request for doctors, but the Taira family abandoned the lock-up policy and let Tsushima continue the tributary trade with Goryeo. They made numerous efforts to expand trade with Song, including arranging a meeting between Song merchants in Japan and the former emperor (father of the then emperor of Japan). Song merchants had the upper hand in the trade with Japan, however, that began to change at the end of the 12th century as the Taira clan, made stronger by its hold on the Dazaifu, intervened. Unilateral trade by Song merchants developed into bilateral trade in which Japanese traders journeyed to Song and engaged in trade.

In order to pave the way for a Japan-Song trade relationship, safe means of sailing and sea routes had to be secured first, prompting the Taira clan to organize domestic water routes. After developing the infrastructure required for ships, the Taira showed a great interest in sea routes to other countries. At the time, the southwestern coast of Goryeo, including the island of Jeju-do, served as an important port for Japan at which Japanese ships could stop in the event of bad weather, get drinking water, and also as an additional trading post on their way to Song. Goryeosa includes records about Japanese merchant ships drifting onto the coast of Goryeo on their way back to Japan from Song or Yuan on several occasions at the end of the 12th century. The safety and protection of Japanese sailors seems to be have been an impetus for the tributary trade.

It seems that the tributary trade relationship lasted at least until 1263. Relations between Goryeo and Japan soured when the Mongol leader Kublai sent a letter to Goryeo demanding its cooperation in making Japan a tributary state of the Mongols following Goryeo’s surrender in 1260. In 1272, just before the Mongolian invasion of Japan, the governor of Gyeongsang province sent back a Japanese ship that had arrived in Geumju out of fear that the newly established Mongolian dynasty Yuan would find out about the connection between the two countries. The ship was most likely from Tsushima Island. Despite the mounting tension in international relations, it was believed that Goryeo and Japan intended to continue their exchange. However, these diplomatic ties were severed in the wake of the Mongol invasion.

The issue of returning castaways from both countries was also of importance in regard to the tributary trade with Tsushima. In the past, Geumju functioned as a port for the ships for tributary trade, a gateway where the Japanese people could pass freely. In the mid-11th century, an official residence for Japanese guests was built in Geumju but the Goryeo government used the facility exclusively for Tsushima islanders who were engaged in the tributary trade and even provided residential districts for Tsushima people in Geumju. For this reason, it was an established practice that the shipwrecked sailors of Goryeo were to be brought from Tsushima to Geumju. In other words, the protocol for the return of castaways had been established, via an official route that connected different locations in Japan with Dazaifu, Tsushima, Geumju, then finally, the Commandery of Southeastern Coast.

When Genghis Khan took power in 1206, the Mongolian empire launched a military campaign to conquer neighboring nations and even brought Goryeo under its rule. In 1260, Kublai, the son of Genghis Khan, sent a letter to Goryeo in which he requested that Goryeo dispatch an intermediary to accompany the Mongol messenger to Japan. In response, the court of Goryeo arranged a party that included Song Gun-bi, the deputy commissioner of the Royal Secretariat, to assume the responsibility of taking the Mongolian representative to Japan. The envoys traveled as far as the Songpo shore on Geoje Island but returned unsuccessful in reaching Japan, blaming the bad whether. The failure of the mission reflects Goryeo’s early attempts to avoid any friction that might incite the Mongols to invade Japan.

Obviously dissatisfied by Goryeo’s attitude, the Mongols again sent Kublai’s letter to force Goryeo to dispatch an envoy to Japan. Goryeo agreed and went to Dazaifu to negotiate, but to no avail. The third envoy delivered the letter but failed to return with any response from Japan. After all, Goryeo did not support the Mongol plan to invade Japan as it meant that Goryeo had to cooperate with preparations for war and face severing its diplomatic relations with Japan. According to the letter delivered by the Goryeo envoy, Goryeo knew that Japan would be suspicious when Goryeo and Mongol representatives arrived together. Given no choice, Goryeo complied with the demands of the Mongols but discreetly prevented the envoys from crossing the sea, again blaming the uncontrollable weather. It was clear that Goryeo was attempting to avoid possible conflict that would arise with Japan in the event of a Mongol invasion.

The Kamakura bakufu, the shogunate that ruled Japan during this period, flatly refused the demands of the Mongol empire stated in its imperial letter and proceeded to prepare for an armed conflict. The royal court in Kyoto wanted to send a response but the Hojo clan, who had actual ruling power over the country, opposed the idea and insisted on a hard-line policy. The bakufu ordered warriors in Kyushu and all the soldiers who held land in that region to build a defense against the Mongol invasion.

Three years after the Mongol empire changed its title to Yuan in 1271, an allied fleet of 900 battleships with 20,000 Mongolians and 7,000 Goryeo soldiers aboard sailed from Happo in Masan in 1274. They landed on Tsushima Island and defeated Japanese forces there before moving on to invade Iki Island. Upon receiving the news from Tsushima, the Dazaifu of Kyushu hurriedly prepared to defend itself but it was unable to fight off the expedition force that landed at Hakata bay. In the face of collective fighting and explosive weapons that the Japanese had never seen, Japanese troops struggled and were pushed back near the Dazaifu. That day the allied forces withdrew and returned to their anchored ships. That night a storm struck the harbor and a large number of ships were sunk and destroyed, forcing the expedition force to return to Happo.

After the first invasion, the Mongol empire dispatched another envoy in 1275 with a message calling for Japan’s subjugation. However, the bakufu killed the Yuan envoy and mobilized soldiers in Kyushu to build a defense wall along the shoreline to protect against another Mongol attack while issuing an order to gather military resources. The bakufu even contemplated a plan to invade Goryeo, but the plan was not carried out.

Outraged at the news of the murdered envoy, Kublai mounted another major offensive against Japan. This time the expedition force was five times bigger than the previous one, including 900 war ships with 40,000 Goryeo and Mongol soldiers aboard and 3,500 ships carrying 100,000 soldiers from Southern Song, which were forced to join the Mongol force in 1279, making the total number of troops involved 140,000, with 4,400 ships. In May of 1281, the allied force left from Happo in Goryeo and marched into Hakata Bay but retreated in the face resistance from Japanese forces. The expedition force then positioned itself on Takashima Island of Hizen Province and awaited the arrival of the Southern Song army. Upon the arrival of troops from Southern Song in June of the same year, the combined force advanced into Hakata Bay and was about to mount a full-scale attack. It was at this time that a second large storm destroyed 4,000 ships and left a mere 3,000 survivors out of the original 140,000 troops. Yuan planned a third campaign but gave up the plan due to uprisings and disturbances in the country.

After going through two wars, Japan remained on guard for a long time. The defense wall built in Hakata Bay of Kyushu was the first line of defense and through the 14th century, the cost of maintaining it was paid by warriors as part of their shared surveillance responsibility. The experience of overcoming a national crisis gave rise to the shinkoku (divine nation) belief among the Japanese people. During the war against the Mongols, shrines and temples across the country conducted rituals to pray for the surrender of foreign enemies and many believed that their earnest prayers had indeed worked, resulting in the great storm that destroyed the allied forces. The concept of a “divine wind” (kamikaze in Japanese) was widely accepted as well as the belief that Japan had divine protection from the gods. Meanwhile, Yuan and Goryeo, concerned about a counterattack by Japan, increased surveillance at strategic points along the coast and improved the guard and defense facilities in Tamna (present day Jeju). In Geumju, the Jinbyeon Fort was established to command the whole shoreline defense system.

Sambyeolcho (Three Elite Patrols) is of historical significance regarding the Mongol-Goryeo invasion of Japan. Sambyeolcho was the central body of the resistance army organized to fight against the Mongol rule on Goryeo. Its base was located on Jindo in Tamna. Sambyeolcho sent a letter to Japan in 1271, declaring itself the authentic government of Goryeo, and asked for aid in exchange for information about the Mongol attack on Japan. The Sambyeolcho troops adopted a systematic guerrilla strategy to stand against the Goryeo royal house that had succumbed to Mongol rule, and they succeeded in creating obstacles to the planned Mongol invasion of Japan. In 1273, Sambyeolcho was defeated in Tamna, their last outpost, by the Mongols and the Goryeo army. But its role as a third party of influence in the Goryeo-Japan relations carries historical significance.

The Mongol invasion of Japan led to a souring of the relationship between Goryeo and Japan. Geumju had been an exchange point for both countries but Happo in the Geumju jurisdiction was the designated departure point for the expeditionary forces invading Japan. Northern Kyushu, which had maintained a close relationship with Goryeo, became the battlefield where the allied forces and the Japanese army engaged in bloody battles. For the following five decades, these areas were turned into defense bases kept constantly on alert and even limited diplomatic interactions such as tributary trade, were completely severed. The people of Tsushima and the Northern Kyushu, who bore the brunt of the invasion, felt fear and anger for the Mongols and Goryeo. Since then, the ruling class, as well as the Japanese public, openly looked down on Goryeo based on their idea of Japan as "the divine land (shinkoku).”

Waegu refers to the Japanese marauders, who pillaged and plundered from the 13th to 16th century in the East Asian seas. The first historical record of the waegu, or Japanese marauders, is an entry in Goryeosa from 1223, stating “Wae attacked Geumju.” From that time on, increasingly more records report Japanese attacks on Goryeo shores. In response to the pillaging of the Japanese marauders, the Goryeo court took diplomatic and military measures to defend itself. In 1227, Goryeo sent an envoy to Japan to demand the suppression of the Japanese marauders. Muto Skeyori, then the deputy governor of Dazaifu, took drastic action by beheading 90 of the most infamous marauders in front of the Goryeo envoy. As for the Japanese marauders who had attacked Changwon in Gyeongsang province and plundered 120 seok of rice from a grain transport ship, the Goryeo government learned that the guilty parties were from Tsushima and pursued them into the islands to retrieve the stolen rice. In the second half of the 13th century, Goryeo sent envoys on multiple occasions to Japan demand that stronger actions be taken to deal with the problem of Japanese marauders.

The Japanese marauders’ attacks were on the decline albeit temporarily during the armed conflicts between Goryeo and Japan which resulted from the Mongol invasion of Japan. In the early 14th century, however, their attacks occurred on a large scale. In 1323, Goryeo beheaded 100 marauders who were ordinary Japanese citizens who had turned into pirates amid social and political disorder in Japan. The incident was a prelude to future marauders’ attacks on the Korean peninsula, which became more rampant.

For a period of some 40 years, beginning with the 1350 entry in Goryeosa that stated “the Japanese marauders’ pillaging started here” and ending with the collapse of the Goryeo dynasty, the Japanese marauders’ attacks reached their peak. At that time Japanese marauders’ boasted vast fleets ranging from 20 ships to 500 ships in the largest examples. The Japanese marauders appeared on the southernmost coast of Geumgang in Chungcheongbuk-do in 1380 with 500 ships carrying more than 10,000 men. It was written that the Japanese marauders’ force was 10 times larger than that of the army of Joseon’s founder Yi Seong-gye, who took on the task of suppressing the marauders as the temporary military governor of three provinces. As seen in this record, the Japanese marauders not only committed piracy but on rare occasions almost threatened the Goryeo royal house. The Japanese marauders made frequent appearances on Goryeo shores, 394 times during some 40 years and sometimes more than 15 times a year. Well armed, the Japanese marauders moved fast on ships and horses. On many occasions they traveled by sea and then up rivers to infiltrate deep into Goryeo territory.

As the attacks of the Japanese marauders began to take place along the Chinese coastline, the Yuan and the Ming dynasties requested that Goryeo take firm action against the Japanese marauders’ pillaging. Goryeo feared that China would use the problem of the Japanese marauders as a means of legitimizing an invasion, and the sense of impending crisis led to diplomatic tension between Goryeo and China. Damage done by the Japanese marauders was not confined to pillaging but also included arson attacks on official agencies, disrupting the local administrative systems. Moreover, residents of coastal villages fled inland away from the attacks of the Japanese marauders 26 leaving hundreds of miles along the coast deserted.

The Japanese marauders came, for the most part, from Tsushima Island. The island had been dependent on the tributary trade with Goryeo for its food supply because its geographical conditions could not adequately support agriculture. However, due to natural disasters, trade with Goryeo fell far short of supporting the islanders, so many turned to piracy. In the late 14th century, when Japan was in the midst of civil disarray due to the conflict between its Northern and Southern dynasties, soldiers organized large fleets based in Tsushima, and attacked grain transport ships to provide military provisions.

In response to the attacks, the Muromachi bakufu merely stated that the Kyoto bakufu was unable to control the pirates since they were from Shikoku or Kyushu, and expressed that it was willing to develop countermeasures. Goryeo dispatched an envoy in 1377 to complain more aggressively and criticize the bakufu’s passive attitude toward the Japanese marauders, saying, “a nation is obliged to govern its people and prevent robbery.” Japan was at a critical junction in its civil war and thus, lacked the central authority needed to control and manage disturbances. Thus, it would be difficult to expect the Japanese government to settle the problems of Japanese marauders through diplomatic negotiations.

The Goryeo government mounted several successful military campaigns against the Japanese marauders, victories include battles by Choe Yeong at Hongsan; Choe Mu-seon at Jinpo; Yi Seong-gye at Hwangsan and Jeong Ji at Gwaneumpo. In the Jinpo battle, with his own invented firearms, Choe Mu-seon destroyed 500 of the marauders’ships which had made inroads into Goryeo. Yi Seong-gye also made the remarkable military achievement of obtaining 1,600 horses of the Japanese marauders. In 1389, Bak Wi led 100 battle ships in an attack on Tsushima and burned down some 300 ships of the marauders and several buildings before returning with 100 Goryeo captives. The Goryeo government’s combined efforts through diplomatic and military channels, its policy of reconciliation towards the Japanese marauders, and the suppression of disturbance in the north and south dynasties gradually reduced the Japanese marauders’ attacks.

Recently, some Japanese scholars suggested a new perspective on the Japanese marauders in late Goryeo. According to these scholars, the Japanese marauders during this period included many Goryeo citizens as well as Japanese citizens who had joined together in pillaging. This view is entirely based on certain sections of historical records such as Seojongsillok (Annals of King Sejong) but careful examination is needed in the interpretation of these records. A small number of Goryeo people of low class or from coastal villages were likely to have acted as marauders and participated in pillage. But it is not a convincing argument to over-emphasize this fact and claim that Goryeo people led the pillaging or formed an alliance with the Japanese, and no conclusive evidence has been found to support this argument. Any attempt at identifying the participants in the pillage and their characteristics requires more comprehensive and accurate historical evidence.