The formation of the current topography of the Korean peninsula and the Japanese archipelago dates back to 10,000 years ago. When the fourth interglacial period began, temperatures increased and the sea level rose. During this period, the Korea Strait, the Soya Strait and the Tsugaru Strait, north of Japan, were formed, dividing the archipelago from the Asian continent. Separated by the sea, Korea and Japan each developed different cultures: a culture characterized by the comb-pattern pottery in Korea and the cord-pattern pottery culture in Japan (also referred to as the Jomon culture). One may justifiably assume that these two cultures, separated by sea, would not have conducted vibrant interaction due to a lack of shipbuilding or navigation skills, archaeological research paints a different picture. In 1969, cord-pattern pottery produced in Kyushu, Japan, was discovered inside the Dongsam-dong shell mound in Busan. Some years later, Korean comb-pattern pottery was found in Koshitaka, Japan. This suggests that humans in the area were already seafaring at this early stage of history. Comb-pattern pottery was also unearthed northwest of Kyushu, and arrowheads and fishhooks carved from Japanese obsidian were found inside the Dongsam-dong shell mound as well, indicating exchanges between the ancient fishermen of the two regions.

By about the 3rd century B.C., agriculture had been transmitted from the southern part of the Korean peninsula to Japan. The transmission of agriculture is invariably accompanied by the transfer of people and culture. Farming skills, from sowing to harvesting, were passed on, along with knowledge about developing farmland and irrigation. And this also led to the immigration of people who were well aware of the changes in the four seasons. The transition to an agricultural mode of production gave rise to the Yayoi culture in Japan, replacing the Jomon culture. Originating in northern Kyushu, this new culture and way of life spread northwards, reaching the northern part of Honshu in a single century. With the advent of agriculture, people formed village communities, and new cultures spread rapidly between communities with a growing exchange of pottery, bronze and iron. The village communities continued to expand as they built diplomatic ties and trade relations, and became regionally integrated.

This integration gave birth to states which were the size of today’s counties. These states were hierarchical societies comprised of differing classes, with the king at the apex. There were also the ruling elite, commoners who were the primary workforce, and slaves whose states had been defeated in war. The king of an agricultural society was responsible for overseeing the economy and well-being of the members of the state and presided over the important rituals of the agricultural community.

The Three Han (Samhan) states were established in the southern part of the Korean peninsula. The three Hans comprised Mahan, Jinhan and Byeonhan, which in their turn respectively consisted of 54, 12 and 12 small communes or tribal settlements, although the Chinese records use the term Guo, meaning country. In the meantime, Buyeo, Goguryeo, Dongye and Okjeo also emerged in the northern half of the peninsula. On the Japanese archipelago, many states sprouted in the form of farming communities in northern Kyushu and other parts of western Japan. It is recorded in the geographical section of the Chinese history book Hanshu (History of the Han Dynasty) that there were some 100 communes founded by the Wae or Japanese on the Sea of Nangnang (East Sea). By the mid-2nd century, the integration of communities became widespread in Japan, forming a single confederated kingdom comprising some 30 communes and centered around the state of Yamatai.

Around the 3rd century, iron emerged as an important medium of exchange between Korea and Japan. In an agricultural community, iron meant power. With the use of iron farming tools and implements, it became easier to prepare fields for sowing and to build irrigation facilities, which led to considerable enhancement in productivity. Iron weapons also brought people distinct superiority in war. At the time, the Japanese did not possess the skills to produce iron and thus imported iron from Korea’s southern regions to make iron implements. Among the Samhan states, Guya (present-day Gimhae) was the center of iron production. According to the articles on Byeonhan in the Book of Wei of the Records of the Three Kingdoms, Guya sold iron to the rest of Samhan, as well as to Dongye, Nangnang and the Japanese states, and that iron was also used as currency. It is believed that the regional integration of the Japanese states in the 3rd century was a result of clashes over iron importation. In short, the political entities in southern Korea and the Japanese archipelago during the Iron Age became closely connected through the exchange of culture and goods.

After the 4th century, the pace of regional consolidations in both Korea and Japan picked up, giving rise to local powers. Goguryeo(Koguryo), Baekje, Silla, and the Gaya confederacy were developing into kingdoms on the Korean peninsula, each establishing a local foothold and integrating small neighboring states. Meanwhile, the Yamato regime emerged in Japan’s Kinai region, replacing the group that had previously ruled northern Kyushu, to grow into the most powerful state in the Japanese archipelago. At the time, the Three Kingdoms of Korea were maintaining a balance in power, despite a series of wars in the course of territorial expansion. In the late 4th century, however, this balance evaporated with the southward campaign of Goguryeo’s King Gwanggaeto. Goguryeo’s main enemy at the time was Baekje and Goguryeo had been temporarily plunged into a national crisis after the Baekje invasion in the late 4th century, during which Goguryeo’s King Gogukwon was slain. Seeking revenge for his predecessor, King Gwanggaeto launched an intensified military campaign against Baekje shortly after his coronation, conquering a large number of Baekje’s fortresses and villages. He seized the capital of Baekje and accepted the surrender of King Asin after receiving the oath of obedience and loyalty he had demanded. In response to this humiliating defeat, Baekje sent Prince Jeonji to form an alliance with Wa Japan in 397 and also joined forces with the Gaya confederacy against Goguryeo as well as Silla, which was being supported by Goguryeo. In 400, Goguryeo’s army of 50,000 troops advanced southward on horseback and on foot and proceeded to defeat the Wa army that had invaded Silla, taking this opportunity to assert military control over the southern part of the Korean peninsula. After this confrontation, Baekje mobilized its navy and collaborated with Wa to attack the Daifang region, only to be met with a disastrous defeat. With Baekje weakened, Goguryeo held a predominant position in the international politics in the 5th century.

The shifts in international politics described above are based on records found in the book Samguksagi (History of the Three Kingdoms) and the inscription on the King Gwanggaeto Stele. The stele was once the source of controversy, because its inscription included a passage that could be interpreted to read as if Wa had sent troops to the Korean peninsula and occupied its southern region. A conspiracy theory cropped up, claiming that the Imperial Japanese Army General Staff intentionally altered the inscription of the stele by painting its surface with quicklime, and alternative interpretations for the text were also proposed. There are still a number of unsolved questions regarding this inscription.

The King Gwanggaeto Commemoration Stele was erected in 414, two years after the king’s death, by his son, King Jangsu. It was built in Gungnae-seong, then the capital of Goguryeo. After the downfall of Goguryeo, the stele was abandoned and forgotten, suffering exposure damage for over a thousand years, until it was rediscovered by local Chinese around 1880. An in-depth study of the inscription did not begin until 1884, when Lieutenant Sakawa Kageaki, an officer in the Imperial Japanese Army General Staff Office, made an ink rubbing of the stele and carried it back with him to Japan. The translation of the inscription completed by the General Staff Publications Office revealed passages stating that Wa Japan had colonized Baekje and Silla and fought against Goguryeo.

The Japanese were very excited with this discovery, claiming ancient Japan’s dominance over Korea, and used it as their historical basis for justifying and rationalizing their policies of aggression aimed at Korea. They argued that the content of the inscription was objective and reliable since it had been written by Goguryeo’s own historiographers, and as a result, it was long considered an irrefutable fact that ancient Japan governed Korea.

The passage in question can be translated as follows:

For a long time Baekje and Silla were subservient to Goguryeo and they paid tributes. In the year Sinmyo (391) the Wa (Japanese) arrived from across the sea and defeated Baekje, [unreadable], and Silla and made them its subjects.

This interpretation, however, was determined to be “incorrect, considering that under the historical circumstances of the period, it was impossible that the kingdoms on the Korean peninsula were ruled by Wa.” Therefore, a different interpretation, that it was not Wa but Goguryeo that colonized Baekje and Silla, gained wide acceptance. The second version seems more feasible given the historical context, but results in a logically awkward sentence structure. Furthermore, the conspiracy theory was disproved following the discovery of an earlier rubbing, procured before the layer of quicklime was applied to the stele, which verified the text of the original inscription.

In light of the facts, the most suitable interpretation of the inscription is as follows:

For a long time Baekje and Silla were subservient to Goguryeo and they paid tributes. In the year Sinmyo, the Wa (Japanese) arrived from across the sea and defeated Baekje and [unreadable] Silla, and made them subjects.

The two unreadable characters in the last sentence formed a verb, not a noun, and the subject of the sentence is Wa. The text intentionally emphasizes the chronology of events, that Baekje and Silla became subjects of Wa only after they had been subjects of Goguryeo. This statement, of course, bears no resemblance to the historical facts.

So why would Goguryeo inscribe Wa’s military achievements on a stele intended to highlight the achievements of King Gwanggaeto? Is the inscription true? If not, what should we make of an inscription, whose text we, as Koreans, find hard to accept? In order to find answers to these questions, we must look to the Confucian political ideology that guided the ruling class of Goguryeo.

Goguryeo adopted Confucianism, began to foster its growth during the reign of King Sosurim, grandfather of King Gwanggaeto, and promoted it as the country’s political ideology by establishing Confucian institutions in addition to various other measures. The aim of Confucian political ideology was to establish a benevolent government based on rule by virtue. Looking at the inscription on the King Gwanggaeto Stele through the lens of Confucian ideology, the middle section of the inscription, which takes up two-thirds of the entire text, illustrates the achievements of King Gwanggaeto in eight articles, each describing the outcome and conquests of the various wars in chronological order. Following Confucian ideology, however, it would likely have been considered inappropriate to record every conquest without justification, considering Goguryeo’s commitment to establishing a benevolent government. Therefore, the inevitability of war—namely, the justification of and rationale for war—was given prominence in order to elevate the image of the conqueror to that of a virtuous monarch.

The campaigns of King Gwanggaeto resulted in a new international order led by Goguryeo as the superior state, giving birth to Goguryeo-centered ideas, similar to China’s sinocentrism and its tianxia (all under heaven) ideology. The inscription on the King Gwanggaeto Stele reflects these ideas. For Goguryeo, the southern part of the Korean peninsula was a target to conquer and subdue. Once Goguryeo had achieved this goal, it shifted the focus away from the conquest onto the fact that this region originally had a subservient relationship with Goguryeo. So by stating that Wa had plundered these states and made them its subjects, then Goguryeo could stake its claim to the moral high ground, claiming to have liberated them from Wa’s control. To justify war and invasion, Goguryeo constructed a fictitious account of a time when the southern part of the Korean peninsula fell under the control of Wa, and used that story to retroactively justify its military operations. For Goguryeo, Wa was not a target of territorial conquest but an alien people that had once fought Goguryeo in support of Baekje.

In short, Wa, as described in the inscription on the stele, was a fiction created by Goguryeo’s historiographers, in order to justify Goguryeo’s southward expansion. Goguryeo did not invent an enemy, preferring to use the existing kingdom of Wa, which it came to know through war, in fabricating material to serve its purposes. Keeping all of this in mind, it must be said that a single passage taken from the full inscription does not quite offer sufficient evidence to conclude that ancient Japan once ruled the southern region of Korea, nor is it appropriate to wholly reject the translation of the inscription as unreliable while offering alternative readings, which would be indicative of potential bias towards one’s own country and history. What is important here is to develop an accurate understanding of the logic and the political ideology behind the inscription. It must be acknowledged that all historical records are influenced by the self-justification of the ruling class in one form or another.

The Gaya confederacy emerged in the region that was home to Byeonhan during the Three Han (Samhan) period. The region covered the area that is now called Gyeongsangnam-do Province, part of Gyeongsangbuk-do, and the eastern part of Jeolla-do. It bordered Nakdong River to the east, Seomjin River to the west, and Mt. Gaya in Hapcheon to the north. Although the Gaya confederacy was later absorbed into the two powerful states to its east and west, Silla and Baekje, the cultural legacy that Gaya left behind reflects its excellence and advancement. Gaya’s superior culture attracted the attention of its surrounding states, resulting in a healthy and active exchange of goods and culture.

Among the Gaya confederacy, Geumgwan Gaya was from early on the most advanced state. It was the most powerful state in southern Gaya, having succeeding Guya in the Three Han period. Geumgwan enjoyed the high agricultural productivity of its alluvial plains around Nakdong River, as well as rich fishery and iron resources, providing surpluses that made active exchange possible with several other countries in East Asia. In the 3rd century, the Wa people in northern Kyushu looked to the Gaya region as a good source of iron. At the time, iron was a medium of exchange that was sometimes used in the place of currency. Iron was found in almost every tomb of Gaya’s ruling class. Iron was a vital resource for a ruler, used to enhance agricultural productivity and in forging weapons. It was in itself a symbol of power, an indispensable material crucial for maintaining kingly authority and establishing government systems.

There is no record that sheds light on the relationship between the Gaya confederacy and Wa around 4th century. In fact, this period has been called “the Mysterious 4th Century” since there are no known records of life on the Japanese archipelago at that time, not even in Chinese literature. All trace of Japan completely disappears from recorded documents after the kingdom of Yamatai offered tribute to Western Jin of China in 266. The political situation in Kyushu therefore is unclear after Yamatai, but even after the decline of Yamatai’s power as a confederated kingdom, the local political body that succeeded Yamatai is believed to have survived. Other Wa powers must have engaged in active exchange with southern Korea as well, since their relations with China had been completely ruptured.

The states of the Gaya confederacy, such as Geumgwan, Taksun and Alla undoubtedly maintained ties with the local powers in northern Kyushu as they had done in the 3rd century. During the excavation of ancient tombs in Daeseong-dong, Gimhae, Japanese-style relics, including pinwheel-shaped bronze implements and jasper arrowheads were excavated from one of the tombs, estimated to have been built in the early 4th century. These relics are evidence of exchange between the ruling classes of Wa and Geumgwan: It is believed that in return for iron provided by Geumgwan, the Wa leader offered rice or ceremonial implements produced in Wa. This form of exchange helped enable political and military cooperation among Baekje, Gaya, and Wa during the southern campaign of Goguryeo’s King Gwanggaeto, which was followed by friendly relations between Baekje and Wa with Gaya as mediator, the dispatch of Wa troops to the Korean peninsula, and unity in the Gaya confederacy.

Between the late 4th century and the early 5th century, the massive military campaign of Goguryeo’s King Gwanggaeto in the southern regions sent all the states in East Asia into turmoil. Goguryeo began to exercise influence over the southern part of the peninsula, a highly sensitive situation that the neighboring states responded in different ways, depending on their own political interests. According to the record on the 10th year of King Gwanggaeto’s reign title Yeongnak (400) on the King Gwanggaeto Stele, Wa frequently violated the border of Silla, and Goguryeo sent 50,000 troops at Silla’s request, attacked the Wa army stationed between Namgeo-seong and Silla-seong (then the capital of Silla), chased them to Jongbal-seong in Imna-gara, and captured the fortress. Meanwhile, Alla sent troops to support the Wa troops against the allied forces of Silla and Goguryeo, only to be defeated. The fact that the Gaya confederacy took military action in cooperation with Wa is important in understanding the historical context of their relationship. This was not the first time diplomatic ties were established between Wa and the two representative states of the southern Gaya, Alla and Geumgwan. Rather, this development was an extension of an existing relationship. Furthermore, the Gaya confederacy is believed to have played a major role when King Asin of Baekje dispatched his son, Jeonji, to Wa to request military assistance. Baekje was able to make this request with the help of the Gaya confederacy, based on the cordial relationship that they had formed beginning in the late 4th century, during the reign of King Geunchogo of Baekje. All this was possible because of the extensive ties between the political groups of the Gaya confederacy and Wa.

Goguryeo’s southern campaign resulted in a tremendous power shift as Goguryeo gained significant influence not only over Silla, but also over a considerable part of Gaya, including Geumgwan and Alla, to the extent that it stationed military troops and exercised sovereign power in those regions. The stir that Goguryeo had caused also had an effect on the Japanese archipelago. Some people from parts of Gaya, including Geumgwan, emigrated to Japanese territories. A recent study suggests that Japan’s Sueki pottery is of the same lineage as Gaya’s ceramic wares, and that it was first produced in northern Kyushu and then moved to Kinki region, which appears to be a consequence of the migration of Gaya potters following the southern campaign of King Gwanggaeto. The migration of Gaya people to Wa regions resulted in the transmission of new technology and information, which greatly contributed to the development of ancient Japanese culture. Some of these Gaya immigrants may have been persuaded to serve the Wa royal house. Some historical records show surnames that resemble the names of Gaya’s sates and regions, such as Alla, Mimana, Gimun, and Dalsa, suggesting the presence of Gaya immigrants. Gaya people’s immigration to Wa and service in the Wa royal court appear to have provided momentum in reinforcing relations between the Gaya confederacy and Wa in the years after King Gwanggaeto’s southern campaign. It seems that the royal authorities of Wa became more interested in the culture of Gaya, and grew attached to the region. This affinity helps explain why the Wa kings advocated the reconstruction of Gaya after the downfall of the confederacy.

In the 6th century, the Gaya confederacy gradually began to be absorbed by Silla and Baekje. In the early 6th century, Gimun and Daesa, located in the downstream region of Seomjin River, came into Baekje’s sphere of influence as Baekje advanced southward. At this time, the Wa regime sent military troops to assist Baekje. Daegaya, a major state in northern Gaya, faced military confrontation with Wa. Why had Wa, which had previously kept friendly relations with the Gaya confederacy, changed its attitude and began to show hostility towards Gaya? This apparent about-face actually reflected the multilateral exchange that took place between the political powers of the Japanese archipelago and Gaya confederacy, meaning diplomacy was not monopolized by a single force, but conducted through multiple channels. The Gaya states along Seomjin River maintained friendly relations with the powers of western Japan around northern Kyushu, while the states in the lower reaches of Nakdong River had an alliance with the Yamato court in the Kinai region.

In 532, Geumgwan Gaya was annexed by Silla, and nearby Taksun was also absorbed soon thereafter. In the 550s, Alla, a major state of southern Gaya, perished, and in 562, Daegaya, the last kingdom of the Gaya confederacy, finally collapsed. All the remaining states of Gaya, in the modern province of Gyeongsang-do, were then annexed by Silla.

The Wa government called for the reconstruction of Gaya, but history had already begun to flow in a direction favorable to Silla. To Wa, Gaya was the source of advanced civilization including iron resources, and cultural exchange between the two powers had evolved into a kinship. The connection between Gaya and Wa was built with iron resources, since iron was the basis of existence for Wa.

The most controversial issue in the history of ancient Korea and Japan is the theory of Imna Ilbon-bu (Mimana Nihon-fu in Japanese), or the Imna Command Post. Imna Ilbon-bu is an outpost allegedly set up by the Yamato regime to rule Gaya. According to this theory of the Japanese conquest of the Gaya kingdom, Japan is said to have ruled Gaya for approximately 200 years, from 369, when the Yamato regime subjugated seven Gaya states, until 562, when its last state, Daegaya, fell.

The sole basis for this theory is the ancient Japanese book Nihon Shoki (The Chronicles of Japan), according to which, the seven major states of Gaya were conquered by Japanese armed forces, as stated in the book’s “Chronicle of Empress Jingu” section, in a passage on the 49th year of the Empress’ reign (369). However, there is no description of the Japanese actually governing Gaya. A section on the 23rd year of Emperor Kimmei’s reign (562) reads, “Silla destroyed the Imna District Office (Gwanga),” followed by this annotation: “Imna fell. The region called Imna as a whole, was composed of the individual states of Gara, Alla, Saigi, Jolma, Gocha, Sanbanha, Geolchan, and Imye.” The term Imna was sometimes used to refer to all of the Gaya states, while at other times it refers to a specific state. Nihon Shoki mentions that Imna District Office controlled all these states, but was later destroyed by Silla. In the book’s passage on the 7th year of Emperor Yuryaku’s reign, the term “Imna guksa (official)” appears and it is understood that this official was dispatched by Japan. The term gwanga is the equivalent of dunchang (miyake in Japanese), a term that referred to a government organization of the ancient Yamato royal house under the direct control of the king. Dunchang was the term reserved for domestic organizations, while gwanga was used for overseas organizations. In other words, Imna District Office (Gwanga) was an overseas governing body under the direct control of a royal house of ancient Japan. The more familiar Imna Command Post, actually refers to the Imna District Office and that, in a nutshell, is the sum total of what we know of the Imna Command Post as described in Nihon Shoki.

But the story doesn’t end there. In 1916, during Japan’s annexation of Korea, the Japanese Government-General launched a five-year plan to investigate historical remains throughout the Korean peninsula. The plan was designed with the goal of verifying the existence of the Imna Command Post. In 1921, after a thorough investigation, Hamada Kosaku of Kyoto University, one of the participants in the study, included in his thesis a statement that prejudice should not get in the way of determining the existence of the Imna Command Post.

More recently, in the 1980s many of Gaya’s remains and relics, which revealed the unique and advanced character of Gaya culture, were unearthed through excavations in Gaya’s cultural belt. The discovery was followed by numerous new studies with differing views on the Imna Command Post. At the time, Japanese scholars were gradually beginning to weigh in on the side of Gaya. Based on the conclusion that Wa was another name used for Gaya, major theories have been developed on the exact nature of the Imna the Imna Ilbon-bu referred to, including that it was a council system organized by powerful clans of Gaya; that it referred to the official that the Wa royal court had dispatched; that it was a diplomatic post that Gaya established for relations with Wa; and that it was a joint council system of Gaya’s king and Japan’s officials organized to maintain Gaya’s independence. Many competing theories were proposed in Korea as well, including ones asserting that Imna Ilbon-bu was a colonial institution established by Baekje, or that it was a group of people who worked to maintain Gaya’s independence.

Almost all of these theories reject the idea of a Yamato occupation of Gaya. This rejection is highly significant in the history of research on Imna Ilbon-bu, marking a turning point in the studies of the history of relations between Gaya and Wa. There is also near consensus that the period of the Imna Command Post’s existence was limited to the 6th century, and that its scope of activity was confined to the regions in the vicinity of Alla. In detail, these theories present different opinions, especially about the functions and the elements of Imna Ilbon-bu, but the general trend is to resolve the Imna Ilbon-bu issue in favor of the Gaya confederacy.

Nihon Shoki, the only surviving historical record that mentions Imna Ilbon-bu, deals with the subject mostly in the chapter on Emperor Kimmei, who reigned in the 540s, with the exception of one other passage in the chapter of Emperor Yuryaku, the content of which is considered by many to be unreliable. Considering that Gaya was then in the process of being destroyed by Silla and Baekje, Gaya’s most urgent task would have been to escape total defeat. This premise is crucial in examining the theories surrounding Imna Ilbon-bu. It is also noteworthy that the Imna Ilbon-bu mentioned in Nihon Shoki is not described as an independent entity but only as part of the “Imna Restoration Conference.” The Imna Restoration Conference was a council for promoting the reconstruction of Geumgwan and other Gaya states that were annexed by Silla in 532. According to Nihon Shoki, despite the Wa emperor’s strong aspirations for the reconstruction of Imna, it was Alla and Baekje that played leading roles at the conference, prominently featuring the intentions of King Seong of Baekje. Some participants appear to have been from Wa, but the conference was an international meeting for the most part, led by the ruling class of the Gaya states and officials from Silla and Baekje. Furthermore, these members of the conference frequently behaved in a way that was counter to the orders of the Wa emperor, which undermines the argument that ancient Japan may have occupied Gaya. Passages of the Baekje-led Imna Restoration Conference mostly appear in Baekje-bongi (Chronicle of Baekje). Baekje was competing over the Gaya states in the 6th century, and historical records on this period naturally focused on Baekje’s relations with the Gaya states. Baekje’s efforts to penetrate the Gaya regions inevitably put pressure on Gaya, and in these efforts, Baekje may have tried to lead the Imna Restoration Conference in the direction that would be advantageous to Baekje. However, this in itself does not explain the nature of Imna Ilbon-bu.

Imna Ilbon-bu officials, who participated in the Imna Restoration Conference, were inclined to hold pro-Gaya, anti-Baekje positions while at the same time failing to side with either Japan or Silla. This independent stance bolsters the case against the theory that Imna Ilbon-bu was the ruling institution of a specific state or power. There can be no other explanation besides the one that the Imna Restoration Conference was a movement in support of Gaya’s wish to gain independence from its neighboring states. Alla was at the center of this movement. Alla, as described in the inscription on the King Gwanggaeto Stele, evolved into a powerful state of the Gaya confederacy between the late 4th century and the early 5th century, and emerged as a rival force against the powers in the Gimhae regions, establishing a strong military force that rivaled those of Goguryeo and Silla. After Geumgwan fell in the 530s, Alla emerged as the leading power among the southern Gaya states, playing a central role in Gaya during its period of decline. Alla also served as the main stage for Imna Ilbon-bu activities, since it was the key force behind the effort for the independence of the Gaya states.

In summary, based on the available evidence, it is reasonable to conclude that Imna Ilbon-bu was a group of people, centered around Alla, who worked for the independence of the Gaya states in the 540s when Gaya was in the midst of a national crisis.

Of the Three Kingdoms on the Korean peninsula, it was Baekje that maintained the closest relationship with Wa Japan. Since they first established diplomatic relations, the two kingdoms of Baekje and Wa remained close until Baekje’s demise in 660. The establishment of diplomatic ties between Baekje and Wa is documented in two historical records: A passage in the ancient Japanese book Nihon Shoki (The Chronicles of Japan) explains how Taksun, one of the states of the Gaya confederacy, acted as mediator between the two kingdoms over a period of several years, between the 46th and 52nd year of Wa Empress Jingu’s reign, and the year inscribed on Chiljido, the seven-blade sword that Baekje sent to the Wa King, reads “the 4th year of Taihe, the era name of the Eastern Jin Dynasty in China (369).” However, these sources are not free of controversy. It is highly likely that Chiljido was created a century after the date inscribed on the sword. The authenticity of the Nihon Shoki is also being questioned, which has led to considerable debate over the prevailing theory that Japan and Baekje established relations in the late 4th century, during the reign of King Geunchogo.

It seems that the kingdom of South Gaya first mentioned Wa to Baekje during the reign of King Geunchogo. The event that finally brought Baekje and Wa together was when Goguryeo’s King Gwanggaeto launched his southern campaign towards the end of the 4th century. According to the King Gwangaeto Stele, in 396 Goguryeo captured 58 fortresses and 700 villages, and proceeded to move on the capital of Baekje, where King Asin was forced to surrender. Faced with the possibility of annexation, Baekje sent its Crown Prince to the Wa royal house with an appeal. The inscription on the King Gwanggaeto Stele provides additional support for this version of events: “Baekje, in violation of its oath, associated and allied with the Wa.” In light of the military threat posed by Goguryeo, Baekje chose Wa as its long-term military ally.

From that time on, trade flourished between the two kingdoms and in the late 5th century, Baekje’s King Gaero sent his brother Gonji to Wa. Gonji set out for Wa in 461 and ended up living there for almost 16 years. It is likely that Gonji was dispatched in order to cement Wa’s pro-Baekje stance. Meanwhile, in 475, Baekje fell into chaos after King Gaero was captured and killed by Goguryeo, and its capital Hanseong had to be moved further south to Ungjin. The already unstable situation was exacerbated when King Munju and King Samkeun were both killed during internal conflicts. It was amidst this turmoil that Prince Gonji’s Japan-born son arrived in Baekje, to be crowned King Dongseong. The cooperative relationship between Baekje and Wa was further secured due in large measure to the pro-Japanese sentiments of King Dongseong,. This affinity led to the development of a mutually beneficial relationship between the two kingdoms that involved cultural exchange and military aid.

Like his predecessor King Dongseong, King Muryeong continued Baekje’s pro-Wa stance in his foreign policy. During King Muryeong’s reign, Baekje expanded south in the direction of Seomjin River towards the region of Gaya. Wa offered military support to Baekje during this time. In return, Baekje dispatched several renowned scholars to Wa, including specialists in the Five Confucian Classics. The era of King Seong, who succeeded King Muryeong, was a time of heated territorial conflicts, which Baekje tried to quell with various alliances and treaties. In his efforts to overcome this crisis, King Seong dispatched scholars adept in philosophy and technology to Wa. Further, his introduction of Buddhism to Japan had a profound and lasting impact on Japanese culture.

What is most interesting about the cultural exchange between Baekje and Wa is that nearly all of the people Baekje sent to Wa were artisans, Confucian scholars, and Buddhist monks. These artisans and thinkers from Baekje, who came to be known as the Imaki no Ayabito, or newly arrived Koreans, would eventually coalesce in the benotami system, Japan’s pre-7th century governing organ. Benotami consisted of various groups of professionals specializing in ceramics, leatherwork, painting, silk weaving, interpretation and other work to meet the needs of the royal house. These benotami artisans were Imaki no Ayabito whose skills had been passed to them by their fathers, a form of inheritance. The benotami’s structure has its origins in Baekje’s naegwan (interior office) system, which was comprised of twelve offices that handled supplies for the royal court, including grain, meat, horses, swords and medicine, as has been described in the Chinese history book Zhoushu (Book of Zhou Dynasty). Benotami formed the roots of a comprehensive production system in the early days of ancient Japanese kingdoms and in order to fully establish and develop this system, Wa required skilled and advanced artisans from outside, and their source was always Baekje.

Baekje gave more than its artisans and production systems to Japan. Baekje also dispatched scholars who were knowledgeable in the fields of medicine, divination, and astrology. Baekje scholars and artisans were sent to Wa in alternating rotations, which indicates that they were professionals prepared to teach various aspects of advanced culture to the Japanese. Meanwhile, monks from Baekje continued to spread Buddhism in Japan, and artisans specializing in Buddhist sculpture and vessels for use in rituals, continued to play a substantial role in the development of Japanese politics and culture.

Meanwhile, in the 640s, military conflict on the Korean peninsula was intensifying and military diplomacy became a matter of increasingly great importance. Baekje’s biggest threat at the time was Silla. Previously, a Baekje-Silla alliance had successfully regained the Han River basin, which had been under the sway of Goguryeo. However, after Silla’s betrayal, Baekje lost the Han River basin again and its King Seong was killed in battle. This loss resulted in fervent anti-Silla sentiments among members of the Baekje regime and Baekje’s King Uija invaded the west of Silla in 641, weakening Silla’s military and gaining leverage. As tensions mounted, the two kingdoms both turned to Wa for diplomatic relations. Silla sent the renowned Kim Chun-chu, but Baekje was ahead of them, having previously sent Prince Pung accompanied by a large entourage. Despite similar minor setbacks, Silla successfully formed an alliance with Tang China’s massive army. And in 660, the joint Tang-Silla forces annexed Baekje.

Baekje ambassador’s message to the Wa royal court, from the 9th lunar month of 660, provided an account of how Silla, with the help of Tang, had invaded Baekje, imprisoned its high-ranking officials, and massacred civilians. Another message from the 10th lunar month of that year asked Wa for help in exchange for 100 Tang prisoners of war. In response, Wa completed its preparation for battle to aid Baekje in the 12th lunar month that same year. The following year, in the 8th lunar month, Prince Pung, who had been residing in Wa, returned as captain of the Baekje restoration forces, with 5,000 Wa soldiers under his command. That next year, Wa sent 100,000 arrows along with other military supplies, followed by 170 warships in the 5th lunar month, and in the third lunar month of 663, a total of 27,000 soldiers were dispatched to Baekje.

From the establishment of diplomatic relations to the ultimate annexation of Baekje, Wa and Baekje maintained close ties through constant communication among the ruling classes. Theirs was not a short-lived alliance of convenience; it was a long-term relationship of cooperation, secured over generations. The relationship between Baekje and Wa is unique in its consistency among others in ancient East Asian history. Their close ties grew out of mutual political need during a period when ancient kingdoms were forming, and as trade flourished, trust and friendship developed between the ruling classes of these two kingdoms.

Japan first appeared on the scene of East Asian history when Wa responded to Baekje’s call for help by dispatching troops to fight Goguryeo’s King Gwanggaeto during his campaign on the southern part of the Korean peninsula. Wa Japan’s forces experienced bitter failure against Goguryeo’s well-organized cavalry. The memory of Goguryeo’s power and dominance took hold in the minds of Wa rulers and would play a major part in shaping its perceptions of Goguryeo.

Wa had developed many trading partners in the southern part of the Korean peninsula as part of its efforts to gain what it lacked culturally and economically. These trade relationships were disrupted by Goguryeo’s southern campaign. Unwilling to engage in direct military conflict with Goguryeo, Wa sought diplomatic relations with Song of Nancho China, one of the Southern dynasties. Wa King Bu (Emperor Yuriyaku) addressed a letter to the Song emperor in which he expressed his enmity for Goguryeo. The letter can be construed as an emotional appeal from the Wa royal house to the Song emperor. However, Wa’s attempts to gain Song’s support failed and the relationship between Wa and China had, in effect, been severed. Wa now relied solely on Baekje as a source for advanced goods.

After the 6th century, Silla experienced a significant growth in power, and started to expand its territory. Silla staked its claim to the land along the Han River and pushed further into the northeast region of the peninsula, an area which had traditionally belonged to Goguryeo. It was around this time that Goguryeo made an unprecedented gesture by dispatching a delegation across the East Sea to Wa. The objective of this delegation was to establish a military alliance with Wa, in light of Silla’s newfound strength. The Goguryeo delegation received an ambivalent response from the Japanese; a mixture of welcome and caution. By all outward appearances, it seems that Wa treated the delegates from Goguryeo with the utmost respect: They built a new guest residence for the visiting Goguryeo dignitaries, as well as a new pleasure boat for their enjoyment. The manner in which Wa received the delegation can be seen as an expression of respect and admiration. Considering that Wa had previously attempted to respond to Goguryeo’s might through diplomacy with Song and that it had no choice but to support Baekje in its struggle against Goguryeo, the delegation must have caused quite a stir at the Wa royal court. The Japanese King’s Imperial Edict offers written evidence of Wa’s cordial relations with Goguryeo.

During Emperor Yomei’s reign (586~587) the Japanese court sent Abenohitoko, its first diplomatic envoy to Goguryeo. This visit on the part of Japan was reciprocal. Later, in year 595, Goguryeo sent the Buddhist monk Hyeja to Wa, where he served as a personal tutor to Prince Shotoku, who “served a full term attending the affairs of the state” as a regent during Empress Suiko’s reign. Hyeja advised the prince on politics and foreign relations as well. He was one of the most eminent scholars of his day, adept not only in Buddhism, but in a wide range of disciplines. The year following Hyeja’s arrival in Wa, the Asuka temple was completed. This temple was the first in Wa to be built in the authentic style of a temple and monastery, and served as the tutelary temple for the ruling clan. Hyeja, the leading figure in Buddhism’s early years in Japan, contributed greatly to developing the faith in the country. His accomplishments are often summed up as follows: “Monk Hyeja helped spread Buddhism and became the pillar of the laws of Buddha.”

The relationship continued to develop in the 7th century. In the 3rd lunar month of the 9th year of Empress Suiko’s reign, (601), the Wa royal house sent Otomonomuragikuhi to Goguryeo. We know that he returned to Wa in the 6th lunar month of the following year and that, on his way back, he visited Baekje, presumably to advise the Baekje king of Goguryeo-Japan relations. This meeting indicates that the Baekje-Goguryeo-Japan military alliance that Goguryeo envisioned in 570 had been established with the cooperation of Wa. In 605, Goguryeo’s King Yeongyang sent 300 gold coins to the Wa king to fund the making of a Buddha statue. In 610, Goguryeo sent monks Damjing and Beopjeong to educate Wa artists and artisans on the use of color and on how to make and use paper, ink and grindstone. Goguryeo continued to send monks of cultural sophistication and artistic talent to Wa over the years. The monk Hyegwan was sent to Wa by Goguryeo’s King Yeongnyu in 623 and he was eventually appointed Sojo, the highest Buddhist position in Japan. Not only Buddhist culture but various other cultural attributes of Goguryeo were passed on to Japan in the early 7th century.

In the course of the robust exchange going on between the two kingdoms, the Wa royal house expressed great admiration for the Goguryeo delegation, calling them “emissaries of the gods.” No other diplomatic delegation from the Korean peninsula had been accorded such honor, which reflected the great amount of respect and camaraderie Goguryeo earned in Wa.

Thereafter, the two kingdoms continued to send and receive emissaries, exchanging important information regarding East Asian politics. This relationship continued until 668, when Goguryeo was annexed by the Tang-Silla allied forces. From the Japanese point of view, continuing ties with Goguryeo would have been politically disadvantageous, since the kingdom was on the brink of annexation under constant attacks from the Tang-Silla alliance. In addition, after the fall of Baekje in 660, Wa had started to feel threatened by the Tang-Silla alliance It was all that the Japanese court could do for its century-old ally to accept the Goguryeo refugees that were able to make their way to its islands.

Due to geographic conditions, contact between Silla and Wa Japan dates back to the early stages of ancient state building. In the "Chronicles of Silla" section in Samguksagi (History of the Three Kingdoms) are found 50-odd articles on the interactions between the two countries prior to the 5th century. Although most of them are about the Japanese forays and intrusions into Silla territory, some articles on the exchange of envoys exist as well. The folklore about General Seok U-ro, which originated during the middle of the 3rd century, indicates that contact occurred between the people of the Uyu kingdom, which existed in present-day Uljin, and the Wa in North Kyushu. According to the folk tale, General Seok, who was in charge of receiving Japanese delegations, offended some of the envoys and was consequently killed. However, his death was avenged by his wife. Although this is close to a legend rather than a historical record, it illustrates what exchanges between Korea and Japan were like during the early period of the ancient state formation.

At the end of the 4th century, Baekje and Wa formed a military alliance as a preventive measure against King Gwanggaeto's southward expansion. Silla, uneasy due to the turn of events, dispatched Prince Misaheun, the son of King Naemul, to Wa in 402. This is presumed to have been a strategic move on Silla’s part to weaken the military alliance between Baekje and Wa and to sway Wa in Silla’s favor. However, Misaheun was detained in Japan, thus proving the resilience of the alliance between Baekje and Wa.

In the 6th century, while there was an active exchange between Baekje and the Japanese regime centered in Kinai, Silla attempted to forge a political alliance with Iwai, the head of the North Kyushu district. This attempt seems to have been a countermeasure against the military alliance between Baekje and the Kinai regime. Although Silla and Baekje acted in cooperation with each other against Goguryeo in the North, relations between the two kingdoms were strained, as both were competing for control over the Gaya kingdom. It was the competition between the two kingdoms that was responsible for the measures both took to align themselves with various powers in the Japanese islands. Also in the 6th century, Silla accelerated its military advance into the Gaya region and finally succeeded in incorporating the kingdom of Geumgwan Gaya into its territory. The Gaya Kingdom, until then, had maintained close relations with Japan. The takeover of the Gaya kingdom further exacerbated relations between Silla and Wa, thus resulting in tension that lasted until the early 7th century.

It was not until 610, when Silla began to dispatch envoys to Wa, that relations between the two kingdoms began to show signs of positive change. The Silla envoys were given a lavish reception, making an exceptional impression. This change in the diplomatic tone taken by the Japanese is believed to have been related to its ties to the Sui dynasty of China. If Wa were to conduct active exchanges with the Sui, it had to secure a stable marine route to China. As Silla was in control of the main passage through which the Japanese would have to sail to reach the Sui, it would have been impossible to ensure safe passage to China. Hoping to foster and maintain diplomatic ties to the Sui dynasty, Wa revised its policies regarding foreign relations, as demonstrated by the extravagant reception ceremony held for the Silla envoys in 610, the 18th year of Empress Suiko's reign. In this way, Wa strived to expand its diplomatic spectrum to cover Silla and the Sui, based on multilateral diplomacy, while withdrawing from the previous diplomatic policy centered on Baekje and Goguryeo.

This served as a momentum for Silla to strengthen relations with the Japanese by providing them with ornate cultural products, mainly Buddhist cultural artifacts. The Seated Maitreya in Meditation at the Koryuji Temple, which has been designated as National Treasure No. 1 in Japan, is also one of the cultural exports from Silla during this time. In the Sui-Tang transition period, Silla continued, more enthusiastically, to pursue diplomatic relations with Wa by having the Japanese envoys dispatched to China return to Wa via the Silla kingdom. In that year, Silla changed the name of its office in charge of diplomatic matters from Board of Foreign Relations (Yeonggaekbu) to Bureau of Foreign Relations (Yeonggaekjeon). Given that the original title of this office was Board of Japan (Waebu), the Board of Foreign Relations was indicative of the expanded reorganization of the office in charge of diplomatic relations with Wa. Such an expansion of the diplomatic office in Silla reflected the greater significance of international diplomacy, including diplomacy toward Wa. As a result of Silla's aforementioned diplomatic strategy, Wa was now able to secure routes linking Japan, Silla, and Tang by land or sea, and could import the high-quality cultural products of Silla and Tang. In summation, the early 7th century saw Silla and Wa succeed in forming diplomatic relations advantageous to both kingdoms by establishing new foreign policies in line with the emergence of the Sui-Tang dynasties.

In 645, the emperor wiped out the Soga clan, which had effectively been ruling Wa through a monopoly of power in the Japanese court, and enacted the Taika Reforms, thus creating the Taika regime which was centered on the imperial family. In the 9th lunar month of the following year, the Japanese emperor sent envoys to Silla for the first time since the creation of the Taika regime. This seems to have been a means of confirming the legitimacy of the Taika regime as well as of establishing the new regime’s attitude toward Silla as amicable. An additional objective of this gesture was to restore, through the mediation of Silla, Wa’s relations with Tang China, which had been discontinued in 632. Meanwhile, in response to the tension surrounding the Korean peninsula, Silla dispatched Kim Chun-chu to the newly established Taika regime in Japan. At the time, Kim Chun-chu was at the height of power in Silla, after having suppressed the rebellion led by Silla’s top official Bidam, who plotted to overthrow the king. Kim's visit to Japan was of a diplomatic nature to ensure and strengthen the Japanese court's pro-Silla policy line. On his visit, Kim Chun-chu left such a strong impression on the ruling class of Wa that he was recorded in the Nihon Shoki (The Chronicles of Japan) as follows: "Chun-chu's features are handsome and graceful while his narrative skill is spectacular."

After consolidating diplomatic ties with Wa, Kim Chun-chu visited Tang China in 648 in order to mediate diplomatic relations between Wa and Tang, carrying with him a diplomatic document sent by Wa to the Chinese emperor. In the following year of 649, Kim Da-su was dispatched to Wa to report the result of Kim Chun-chu's trip to Tang China. The Silla envoys dressed in Tang-style wardrobe during their visit to Wa in 651. This was a politico-diplomatic offensive to show Silla's supremacy over Japan, having the authority of Tang as backing. Demonstrating the solid ties between Silla and Tang forced Wa to enter into a political and military alliance with Silla beyond the simple relationship of cultural exchange.

In 654, certain events obliged Wa to clearly delineate its diplomatic policy. Tang emperor Kaozong ordered Wa to send troops to support Silla in case of attack by Goguryeo and Baekje. Wa refused to acquiesce to the emperor’s request and join the Silla-Tang alliance and instead attempted to form close relations with Baekje and Goguryeo, which had been relatively inactive in terms of international relations. The massive military offensive launched by Tang on Goguryeo in 655 brought about a sense of crisis in the Japanese court. In response, Wa built large-scale military installations to protect Asuka, the first imperial capital of Japan. Uneasiness in the Wa royal house was further compounded by the belief that Tang and Silla harbored hostility towards the Wa. Meanwhile, Tang refused to cooperate with Wa's dual diplomatic strategy that entailed access to Tang while at the same time maintaining ties with Goguryeo and Baekje. Silla, aware of Tang's tremendous military power, tried to conform to Tang's diplomatic policy and thus stay in its good graces. This is why when Wa asked Silla to let Japanese envoys accompany Silla envoys on a visit to Tang in 657, Silla refused the request.

Two years later, an incident occurred in which Japanese envoys dispatched to Tang were detained in Tang. Nihon Shoki (The Chronicles of Japan) refers to a book by Ikinomuragihakato which mentioned that Tang issued an imperial mandate stating, "This empire will certainly attack the Korean peninsula next year. You Japanese will not be able to return to your country," and then proceeded to detain the envoys. This action resulted from the belief that Wa was siding with Goguryeo and Baekje and would therefore form a military alliance with the two kingdoms. It was, in fact, a preventative measure to protect Tang’s military secrets.

After the 7th century, Silla initiated aggressive diplomatic outreaches to Wa, providing Wa with cultural products from advanced neighboring countries. This was, in actuality, a means to hold Baekje, with whom relations were antagonized, at bay. After Silla’s plan succeeded, and a promise of military cooperation from Tang was obtained, Silla was able to force Wa into an alliance. As a result of this strategy, Silla defeated Baekje in 660, and then Goguryeo in 668, finally succeeding in unifying the three kingdoms. It can be said that this victory was the result of Silla’s diplomatic strategy of Silla, which utilized international relations in an effective and tactful manner.

The allied forces of Silla and Tang defeated Baekje and Goguryeo(Koguryo) in 660 and 668, respectively. However, contrary to Silla’s original intentions, Tang attempted to establish control over the occupied territory, installing the Ungjin Commandery in Ungjin and the Andong Duhufu ("Protectorate General to Pacify the East") in Pyeongyang. In response to this, Silla decided to wage a war on Tang, and to avoid fighting a two-front war, it dispatched an envoy named Kim Dong-eom to Japan and reestablished its diplomatic relations with the country in in the 9th lunar month of 668. At that time, Japan, in the midst of a domestic crisis made worse by the defeat at the Battle of Hakusukinoe, was striving to build a defensive network as preparation against possible attacks from the Silla-Tang allied forces, by constructing mountain fortress walls and placing military forces on the coast. On the part of Japan, restoration of diplomatic relations with Silla was also needed to stabilize the ruling system within the country. Thus, these restored relations lasted until 779, when official exchange between the two countries ceased. During this period of time, Silla dispatched its envoys to Japan a total of 46 times and received Japanese envoys 27 times.

In the late 7th century, Silla maintained a hostile attitude towards Tang, launching battles against Tang in an attempt to oust the Tang forces from the Korean peninsula and at times, simply maintaining distance from Tang. Japan also focused on exchanges with Silla while maintaining its diplomatic break with Tang till the end of the 7th century. These two countries were in a civil coexistence, engaging in relatively peaceful exchanges while being mindful of Tang. The most notable of the exchanges between the two countries during this era was the spread of Silla's culture into Japan. For Japan, Silla was the only pathway by which it could gain access to the more advanced cultures of other countries. Japan concentrated its efforts on learning from Silla in the areas of law, Buddhism, scholarship, thoughts, etc. for the purpose of establishing the ritsuryo state ("state with law"). The length of the Japanese envoys' stay in Silla was more than two times that of the Silla envoys’ stay in Japan. One may extrapolate that after finishing their official duties, the Japanese envoys would stay in order to learn about Silla culture, the various systems and ideologies of Silla as well as to tour workshops. Given this, it can be said that the Japanese ritsuryo state was based on or influenced by the exchanges with Silla in this period.

Entering the 8th century, Japan began to take high-handed political action against Silla. After establishing the ritsuryo state, exemplified by a central administration and an imperial court system, Japan inserted into the ritsuryo code an article that defined Silla as its tributary state. This article was the manifestation of the sense or rivalry and consequent need for superiority that Japan felt which would also manifest itself in the diplomatic arena. For example, Japan requested that envoys from Silla bring credentials, or to dispatch only high-ranking envoys to Japan. In response to this, Silla took stern measures against Japan, neglecting such requests and refusing to receive Japanese envoys to Silla on the grounds that they were impolite. This is how diplomatic friction often arose between the two countries during this period.

Despite these conflicts, Silla focused on trade with Japan, based on its high production capacity and excellent handcraft skills. Numerous products made in Silla as well as foreign goods imported through Tang were brought into Japan. In 752, Silla dispatched to Japan a delegation of 700 envoys, which was led by the chief envoy Kim Tae-ryeom, for the purpose of not only diplomatic negotiations but also to trade with Japan. At the time, Japan was in need of a number of resources and materials to support the expansion of its national structures and the construction of state-funded Buddhist temples. As if to reflect the Japanese aristocrats' high cultural consciousness, there was a high demand for a variety of luxury products imported from Silla. “Baishirakimotsuge (List of Procurements from Silla),” which was submitted to the government by Japanese officials and aristocrats for purchasing goods from Silla, lists products, along with their prices, such as dinnerware, carpets, Buddhism-related products, medicines, spices, and glassware. The relics presently housed at the Shosoin repository, the treasure storehouse at Japan’s Todaiji temple, are testaments to what the economic and cultural exchange between Silla and Japan was like at the time.

Despite all this, after 779, official exchanges between the two countries came to an end. In late Silla, conflict and struggle within the ruling class intensified and this, coupled with the rise in power of the local gentry, made central control of the country more difficult. The 9th century saw a rise in the number of Silla people going to Japan and merchants engaged in private maritime trade with the Japanese like Jang Bo-go. These people actively traded with Tang, while traveling to Japan to engage in private trade and exchange with the aristocrats in the capital as well as the gentry in Kyushu. The Japanese royal house then adapted a policy barring this kind of trade and exchange, for fear of a union forming between Silla and the local forces in Japan. Since then, Japan began to exhibit an increasingly more hostile and isolationist attitude towards other countries.

Balhae was founded in Goguryeo(Koguryo)’s former territory by Dae Jo-yeong, who united the former people of Goguryeo and the Malgal (Mohe) tribe with the goal of carrying on the the Goguryeo legacy. This kingdom was at first named the kingdom of Jinguk but later came to be called Balhae when Tang China recognized Dae Jo-yeong as governor of Balhae in 713. Balhae's exchange with Japan started with the dispatch of envoys to Japan in 727 and continued until the kingdom’s fall in the early 10th century. In 726, during the reign of Balhae's second king Mu, the neighboring Heishu (Black-Water) Malgal tribe dispatched an envoy to Tang via a route through Balhae territory. Tang then attempted to subjugate Balhae by establishing a colony in the territory of the Black-Water Malgal tribe. After this attempt by Tang, Balhae’s relations with Tang took a turn for the worse. Balhae’s dispatch of its envoys to Japan was aimed at keeping Silla in check, based on the judgment that Silla’s ties with Tang could pose possible threats for Balhae.

Balhae dispatched envoys to Japan 34 times, while Japan sent envoys to Balhae 13 times. Given the dangerous conditions of sailing at the time, which often involved shipwrecks and drifting away in storms in the East Sea, a total of 47 exchanges between the two countries within Balhae’s 229 years of existence serves as a testament to how close the relations were between the two.

In the years following the dispatch of Go In-ui to Japan in 727 until 763, Balhae solidified its alliance with Japan by actively encouraging exchange. Balhae claimed to be the only successor kingdom of Goguryeo and went on to inform Japan of events in China such as the An-Shi Rebellion. During the period of exchanges between the two, Japan attempted to invade Silla, while Balhae took full advantage of Japan's interest in the Korean peninsula, thus benefiting from and solidifying its ties with Japan.

In the late 8th century, when the political situation in China had stabilized, Balhae initiated aggressive diplomatic efforts towards neighboring countries, which resulted in diplomatic friction with Japan. In 771 when Balhae sent its envoy Il Man-bok to Japan, it sparked a feud with Japan by claiming that Balhae was God’s kingdom and calling Japan its nephew country in its credentials. In addition, Balhae continued to use the northern route, ignoring Japan's requests that Balhae envoys pass through the Tsukushi area to reach the diplomatic outpost of Dazaifu. Conflict also arose over the frequency of the envoys’ visits, Japan suggested a visit every 12 years, while Balhae demanded more frequent visits. These disagreements, however, ended with Japan acquiescing to Balhae’s demands. Japan stopped insisting on the Tsukushi route and set up a guest house for envoys from Balhae on the Noto peninsula, the disembarkation point for the northern route, and did not attempt to limit the frequency of Balhae envoys' visitations. After settling these conflicts in the late 8th century, Balhae continued to send envoys to Japan.

The exchanges between Balhae and Japan proceeded as Balhae desired, because Japan did not want to stop benefiting from its exchanges with Balhae and Balhae continued to take advantage of Japan’s interest. Firstly, Japan could access the Chinese and keep in contact with the major figures of Tang through Balhae. In 894, when the dispatch of Japanese envoys to Tang was officially ceased, Japan had to rely on Balhae for exchange with China. Secondly, the Japanese could get precious goods through envoys from Balhae. Balhae’s main export to Japan was furs, and besides this, many items, such as seafood, ginseng and honey, were traded between the two countries. Even the Japanese royal family bought Balhae’s goods, while the aristocrats were involved in direct trade with Balhae envoys. Sometimes Japanese demand for Balhae’s products was too high and the Japanese government had to implement a means of managing imports but this did not affect the exchanges with Balhae.

In addition to political and economic exchanges, the two countries engaged in cultural exchange as well. In particular, the exchange of poetry written in Chinese, which began after the 9th century, can be called the most notable of the cultural exchanges between the two countries. Balhae sent such renowned literary figures as Yang Tae-sa, Wang Hyo-ryeom and Bae Jeong as members of a delegation of envoys to Japan, and some of Japan’s leading writers of the time, including Sugawara Michizane, Oe Asatsune, and Simada Tadaomi, were present at the banquet to welcome Balhae’s envoys. Balhae music, which was played at the banquet for the Balhae envoys, was included as part of a repertoire of foreign musical pieces in Japan’s royal court.

Through such aggressive and adroit diplomacy, Balhae turned its diplomatic ties with Japan into an advantage and engaged in a wide range of exchanges in culture, economy, politics and other fields.