Deciphering historical records has become the cornerstone of comprehending pre-modern East Asian history. In recent times, international relations theories, including the balance of power, have been employed to assess their explanatory power in East Asian international relations and, more broadly, their applicability to the real world to deepen our understanding of how the world works. The prevailing approach to understanding the East Asian version of international relations before the 20th century centers on a unique structure of tributary relations, which typically entails China-led diplomatic relations with other states. However, the nature of the international system reflects structural factors that shape each statés interest-driven behavior within the system.

Recent scholarly works have made significant strides in revealing that traditional East Asian relations encompassed a wider spectrum of forms: 1) a unified Chinese empire as the unipolar power on the Chinese continent, wielding hegemonic influence through its overwhelming political, economic, and cultural capabilities, 2) divided empires on the continent (typically non-Han dynasties in the north and dynasties with Han nation in the south) forming a bipolar order, and exhibiting relatively limited influence and primarily assuming the role of a normative “big brother,” 3) a multipolar order characterized by multiple competing dynasties.

During the early period of the Goryeo Dynasty (918 AD - 1170 AD), international relations in East Asia exhibited a remarkable dynamism, driven by the fluctuations of power struggles within the broader East Asian landscape. Following the Tang Dynasty's three centuries of prosperity, the Five Dynasties and Ten Kingdoms Period (907 AD - 960 AD) was marked by recurrent wars and power transitions, which also ushered in the Khitan Liao Empire, which entered northern China after occupying the Sixteen Prefectures (燕雲⼗六州). The Han-led Northern Song Empire in the south established a border around present-day Beijing, leading to confrontation and conflict with the Khitan Liao. The Khitan's military superiority thwarted the Song's territorial expansion to the north. The war between the two empires in 1004 culminated in the Chanyuan Treaty (澶淵之盟) in 1005, which signaled the Song's weaker position relative to the Khitan and the erosion of the Han-centric worldview (Yun 2015, 142). By providing annual tribute payments of 100,000 taels of silver and 200,000 bolts of silk to the Khitan, Northern Song relinquished its position as both the normative and actual hegemon in East Asia. While the Northern Song Dynasty lost its “big brother” status, the treaty effectively “prevented a potential source of conflict from developing into a major military confrontation” (Yun 2015, 142).

Despite Song's perceived weakness revealed in the Chanyuan Treaty, Goryeós triumph over Khitan Liaós four military incursions into the Korean Peninsula fundamentally altered the East Asian geopolitical landscape for over a century. The Goryeo-Khitan Wars from 993 to 1019 granted Goryeo greater autonomy and independence in its foreign policy decisions and enhanced its standing within East Asian relations (Yuk 2011). Following its victories against the Khitan Liao, Goryeo reclaimed the newly integrated territory south of the Amnok (Yalu) River, which had been previously established by an agreement between the two dynasties in 993. Furthermore, Goryeo capitalized on its strengthened position in foreign relations by formalizing diplomatic ties with Khitan Liao, a move that signified mutual recognition of each other as independent states. Simultaneously, Goryeo maintained cultural and economic exchanges with Song. Despite Song's diminished influence in official diplomatic relations with Goryeo, it preserved unofficial ties to counterbalance the Khitan threat. In 1068, Song restored official relations with Goryeo, elevating the diplomatic status of Goryeós envoy as Guksinsa (國信寺), indicating that Goryeo held the same level of diplomatic priority as Khitan (Song Shi juan 487 liezhuan 246 waiguo 3 Gaoli). Coupled with Song's urgent need to maintain ties with Goryeo to counterbalance the Khitans, Goryeo emerged as a crucial balancing force that significantly influenced the dynamics of East Asian international relations during that era.

In the 12th century, the Jurchens (⼥眞) from present-day Manchuria embarked on a campaign against the Khitans, driving them out of the Chinese mainland and ultimately establishing the Jin Empire (⾦ 1115 AD – 1234 AD). The Jurchens captured the last Liao emperor, Tianzuo (天祚帝 1101 AD – 1126 AD), and in the same year declared war on the Song. Subsequently, without any significant military confrontations, Goryeo and the Jin established peaceful relations based on a “master-servant” dynamic in 1125.

This development is puzzling for several reasons. Firstly, amidst the rapid political turmoil, the Jurchens dispatched envoys to Goryeo with the intention of formally establishing diplomatic relations. While it is conceivable that the Jin sought to contain Goryeo to facilitate their military campaign against the Song, what prompted Goryeós swift acceptance of Jin's offer? In other words, why did Goryeo choose to adopt the role of “servant” to Jin instead of maintaining neutrality during Jurchens' conquest of the Chinese mainland, a strategy that could have allowed both Song and Goryeo to balance against the Jin?

Another perplexing aspect of this development is that, prior to the establishment of formal diplomatic relations between the two dynasties, Goryeo, with its strengthened military capabilities and victory over the Khitans in the 11th century, could have considered a more aggressive policy stance towards the Jin Empire. However, the Goryeo court opted against engaging in military conflict with the Jin. The fact that Jin's military prowess, which had proven decisive against the Khitans, could not entirely explain Goryeós policy choice further highlights this enigma. In 1104, 22 years before the establishment of relations, Goryeo had emerged victorious in military campaigns against the Jurchens, potentially emboldening the dynasty to consider a more assertive approach to the Jin's rise. Additionally, while the campaign against the Jurchens in 1104 established Goryeo-Jurchen relations as “parent and son,” the renewed Goryeo-Jin relations established in 1125 underwent a drastic transformation, with the Jin assuming the role of “master” and Goryeo the role of “servant.” Despite domestic opposition against the court's “mortifying” decision-making and the absence of any imminent threats of invasion from Jin, the Goryeo court chose to submit, relinquishing its position as “father” to assume the role of “servant.” This sequence of events raises the question of whether Goryeós adoption of the subservient role was part of a strategic approach.

This article offers two theoretical implications. Firstly, while the modern form of international relations is widely regarded as having emerged from the Treaty of Westphalia, there has been a growing body of research exploring historical contexts through the lens of international relations theories, including ancient Greek city-states and the Warring States Period in China. These studies have successfully applied and tested explanations of balance of power and bandwagoning. This approach also necessitates investigating international relations in Asian history to further examine the applicability and generalizability of international relations theories across time, ultimately enhancing the overall applicability of these theories.

Historians have attempted to analyze Korean historical events through the lens of East Asian international relations theories. However, the application of these theories to the past has been limited, primarily focusing on wartime dynamics and balance-of-power scenarios, such as the relationship between the Khitan Liao and Goryeo dynasties. During the period of divided empires in China and Goryeós existence in Korea, state behavior was characterized by a complex interplay of balancing and bandwagoning strategies, rather than solely balancing against one another. This challenges the prevailing notion that balance of power was the sole policy option for states in East Asia, particularly in the case of Korea when examining Sino-Korean relations during the early Goryeo period. To safeguard its national interests, the Goryeo dynasty employed strategic bandwagoning tactics in its dealings with both the Liao and Jin empires.

Secondly, Goryeo, as an integral part of the East Asian international system, exhibited a wealth of interactions with other regional powers, revealing patterns of state behavior that can be analyzed through the lens of balance-of-power and bandwagoning dynamics. By examining these interactions, this paper aims to broaden the discussion on the applicability of international relations theories in explaining the realities of traditional East Asia. Furthermore, if such efforts to uncover state behavior through theoretical frameworks prove successful in the East Asian context, particularly in the Korean case, it would be noteworthy to identify any discernible trends or patterns in South Korea's foreign policy, both past and present.

The balance of power theory has widely been accepted in the area of international relations to explain how the world works in conjunction with state behavior. Hans Morgenthau sees balance of power as both a distribution of power among states that try to maintain stability and “a result of a struggle for power where every state must aim for superiority” (Anderson 2018, 8). After that, scholars have tried to examine the causal relationship between the international structure and state behavior in terms of balancing and bandwagoning. Waltz set the assumption that power disparity and state instinct of survival encourages states either to balance against the stronger state or bandwagon to ally with it (Waltz 1967, 215). He further states that balancing is the basic rule of states as a state behavior that is induced by the anarchic international system (He 2009, 115-116).

Walt's balance of threat theory, which centers on state behavior driven by threat perception, distinguishes between balancing, which involves forging alliances against a perceived threat, and bandwagoning, which entails allying with the very threat itself. Walt contends that balancing is more common than bandwagoning due to shared interests among states in resisting a common adversary (Walt 1988, 314). Echoing this perspective, other scholars posit that weaker states are more likely to adopt balancing strategies when confronted with a threat of comparable strength but may remain neutral or bandwagon when facing a significantly more powerful adversary (Rothstein 1968; Levy 1989). In contrast, some argue that states are more inclined to bandwagon rather than balance against a superior power, citing the concept of “deficient power” as a driving factor (Rosecrance and Lo 1996; Murphy 2010).

An alternative perspective posits that state behavior stems from a complex interplay between stronger and weaker states, suggesting that balancing and bandwagoning are neither mutually exclusive nor the sole diplomatic option available. Stephen Walt (1990) maintains that weaker states may choose to bandwagon with a great power due to fear of punishment, the prospect of rewards, and a lack of viable alternatives. This argument highlights the significance of state perceptions; the decision to balance or bandwagon is heavily influenced by the degree of perceived threat. When a more powerful state signals its intention to maintain a non-threatening military presence, weaker states may perceive balancing as unnecessary. Conversely, if a powerful state increases unilateral actions or gestures that pose a threat to weaker states, the latter may opt to bolster their capabilities to ensure their security (Wivel 2008, 301-302). States can engage in “limited bandwagoning,” selectively choosing the areas or extent of cooperation with great powers (Kuik, 2008). This pragmatic approach allows a state, for instance, to strategically align militarily with a great power while maintaining economic and other non-security ties with another power (Vaicekauskaitė 2017, 12).

Recent literature introduces the term hedging extensively to describe a state’s strategic ambiguity in foreign policy choice by sending mixed signals to avoid risks from pursuing balancing or bandwagoning. This may explain a wider range of state behavior, but such policy choices are deeply affected by the international system. According to Koga, hedging is rarely employed in a bipolar world since weaker states face “difficulty in maintaining strategic ambiguity or neutrality and are compelled to engage in either balancing or bandwagoning” (Koga 2017, 7). As hedging is an emerging concept to explain a multipolar system such as the contemporary global environment, the concept is not likely to be applied to 12th century East Asia.

The most prominent argument about possible state orientation and motivation for choosing bangwagoning is well explained by Randall Schweller as following.

“(A)ll sides in the debate have mistakenly assumed that bandwagoning and balancing are opposite behaviors motivated by the same goal: to achieve greater security. In practice, however, states have very different reasons to choose balancing or bandwagoning. The aim of balancing is self-preservation and the protection of values already possessed, while the goal of bandwagoning is usually self-extension: to obtain values coveted. Simply put, balancing is driven by the desire to avoid losses; bandwagoning by the opportunity for gain.” (Schweller 1994, 74)

Scheweller highlights in his argument that the policy choice between balancing and bandwagoning is not solely focused on security threat but profit. This opportunistic choice as a state response to emerging threats, can be effective in bringing peace, less costly compared to balancing, and is likely to result in gain when the international order is distinguished by conflict (Schweller 1994, 93). Again, balancing and bandwagoning are not the opposite behaviors but selectively pursued by states for their policy choice with different orientations to seek their profit and recognition of the international system they are faced with.

Scheweller addresses the motivations behind bandwagoning, arguing that states seek to exploit potential benefits by aligning themselves with the revisionist power challenging the existing order (Schweller 1994, 94). For weaker states, partnering with the revisionist power can provide opportunities to expand their influence, potentially leading to territorial gains. Moreover, these alliances can offer protection from the stronger revisionist state, while simultaneously discouraging the formation of coalitions against it. Another driving force behind bandwagoning is the perception of the “wave of the future.” Weaker states may recognize the rising influence of the revisionist power as an inevitable trend or movement, leading them to seek alignment with this emerging power, particularly if it is perceived to be on the path to supplanting the existing dominant power (Schweller 1994, 96-97).

The application of balance-of-power theory to the study of international relations in the early Goryeo period has gained traction among scholars. This perspective stems from the recognition that pre-modern East Asian actors adhered to a common diplomatic style rooted in investiture and tribute, and that the balance-of-power dynamic shaped the international system in which the Goryeo dynasty was embedded (Lee 2008; Jang 2014; Wang 2013; Yuk 2011; Yun 2011). These scholars argue that East Asian states were often compelled to adopt a balancing foreign policy in response to the prevailing balance-of-power dynamics. Expanding on this notion, Lee Jae Seok (2008) posits that Goryeo employed an eclectic strategy, aligning with third parties to balance or bandwagoning with major powers, emphasizing the preference for balancing over bandwagoning in foreign policy decisions. This implies that balancing and bandwagoning were viewed as distinct, opposing, and mutually exclusive options that could not be pursued interchangeably.

An overemphasis on balancing as the sole explanatory framework for Sino-Korea relations can obscure the intricate dynamics of these interactions, which were influenced by a complex interplay of political, economic, and cultural factors. Much of the existing literature on Sino-Korea relations with the northern empires in the early Goryeo period disproportionately focuses on the occupation of six prefectures east of the Amnok River following the 993 diplomatic negotiations between Goryeo and the Liao and the subsequent 30-year war.

Contrary to the prevailing notion that East Asian states were perpetually engaged in aggressive foreign policies, Khitan Liao maintained diplomatic and security ties with 59 states, highlighting the prevalence of the tributary relations system (Liaoshi juan 36 bingweizhi xia shuguojun). It is noteworthy that Goryeo, after a 30-year conflict with the Liao, established a formal, peaceful partnership through tributary relations that lasted for another century without any major wars (Yuk 2011, 12). This historical view of Sino-Korea relations during the conflict period stems from a biased perception that Goryeós balancing against the Liao resulted in its victory and emergence as a middle power with strong independence and an autonomous foreign policy (Chun 2011, 182-183). Another significant issue arising from this approach is the lack of due attention paid to the continuity of peaceful relations between Goryeo and the Jurchens for 100 years following the centennial Goryeo-Liao relations. This peaceful period stands in contrast to the emphasis placed on the conflictual aspects of early Goryeo-Liao relations.

Advocates of the balance-of-power theory often attribute the “sudden” rise of the Jurchens in 12th-century East Asia to a disruption in the region's balance of power dynamics. However, this perspective overlooks the complexities of state behavior during this period, particularly the actions of the Song and Goryeo. Contrary to balancing against the Jurchens, the Song formed a strategic alliance with them and engaged in an invasion of the Khitan Liao. Conversely, Goryeo adopted a neutral stance throughout the power transition from Khitan Liao to Jurchen Jin, opting for diplomatic relations rather than military engagement (Yun 2015, 155). The balance of power theory struggles to explain Goryeós decision to forego an anti-Jin military alliance with the Song in favor of diplomacy.

Park Yun-mi (2011) viewed the establishment of Goryeo-Jurchen relations as integral to the formation of a new East Asian international order dominated by the Jurchens. Kim Soon-ja (2012b), analyzing Goryeós actions to control the eastern Amnok River region, focuses on the initial relationship between Goryeo and the Jurchens from the perspective of territorial disputes. Kim Bo-kwang (2019) presents another significant work on the diplomatic relations between the two states, asserting that Goryeós foreign policy sought its interests through a realist lens in international relations, examining Goryeós response to changes in the international landscape.

Kim's application of realist theory to pre-modern East Asia is a significant contribution to the field. However, there are various subcategories of realism that can be employed to further enhance our understanding of state behavior, particularly with regard to the motives and actions underlying foreign policy decisions. Classical realism, as utilized by Kim in his work, centers on evaluating individual states based on an understanding of human nature. Structural realism, a refinement of classical realism, views individual states as units within a structured international system. Within this framework, states are driven by self-interest, and their capabilities are both distributed and constrained by the system's structure. Given that Goryeo was not the sole player or game changer in the international arena during this period, it is essential to clarify the motivations behind its foreign policy choices under the structural constraints imposed by the international system if we are to fully comprehend its foreign policy through a realist lens. In that context, the following will examine the changes in the international environment with the emergence of the Jurchens as a revisionist power and Goryeós subsequent decision to bandwagon with them.

When Khitan invaded Goryeo in 993, Goryeo and Khitan established an agreement on setting a border line along the Amnok River, whose south bank was incorporated into Goryeo’s territory and north bank into Khitan’s. In the northern frontiers facing Khitans and Jurchens, Goryeo built six prefectures, namely Heunghwajin (興化鎭), Tongju (通州), Guiju (龜州), Gwakju (郭州), Yongju (⿓州), and Cheolju (鐵州). Later, Liao invaded Goryeo with 400,000 troops in 1010 with the target of capturing the capital city of Gaesung and King. King Hyeonjong (顯宗 1009~1031) of Goryeo had to flee to the south and make a reconciliatory gesture to the Liao, while military officials in the north engaged in rear attack against it. After this failure to achieve Goryeo’s full surrender, Khitan Liao again invaded Goryeo with 100,000 troops but was seriously defeated in Guiju. This time period of war has been referred to as a major victory against China in history education in South Korea, and the significance of the war is that the newly established territory - south of the Amnok River, has become a border line between China and Korea since then.

After the war of 1019, Goryeo and Khitan Liao restored diplomatic relations. In the tributary relations between the two, the Goryeo Dynasty adopted Khitan’s era name (年號) and abandoned official relations with Northern Song. Despite the victory against the Khitans, this diplomatic choice by Goryeo can be seen as a pragmatic approach to increase autonomy in the Khitan-led international relations while still maintaining exchanges with the Song in Southern China. In this international setting, Goryeo was able to gain prosperity and peace without engaging in a large-scale war. Nevertheless, Khitan Liao established a settlement named Boju (保州) in the southern bank of the Amnok River in 1014, which ignited a territorial dispute lasting for a century (Kim 2012a, 142).

Boju, the heart of the tension, is today’s Shinuiju of North Korea connecting China at the border line. The city was a major transportation route for trade, and also served as a military and diplomatic hub. In 1005, in violation of the agreement that recognized the southern area of the Amnok River as Goryeo territory, Khitan Liao established a state-run trading post (榷場) at Boju. This move was an attempt to expand Khitan's political and economic influence and exert control over Goryeo and the Jurchens. Goryeo viewed this action as a trespass and a breach of the 993 agreement. Considering the establishment of similar trading posts in border regions neighboring Song and Western Xia, it becomes evident that Khitan's occupation of Boju was part of a broader strategy to solidify their position in the international order by forging economic partnerships with neighboring countries while simultaneously reinforcing their military capabilities by seizing strategic locations (Kim 2021).

Jurchen's ascent as a rising power signaled a revisionist force within the Khitan-dominated East Asian international order. Internal political unrest and revolts plaguing the Khitan Liao empire starting in the 1030s under Emperor Xingzong (興宗) presented a unique opportunity for the Jurchen tribes, previously fragmented and lacking central leadership, to further their unification process. This rise initially brought them into conflict with Goryeo. Wars between Goryeo and Jurchen in 1004 and 1107 culminated in victories for Goryeo and a territorial expansion towards the northeast. However, this proved to be a mixed blessing. While unified Jurchen, under the leadership of the Wanyan Tribe (完顔部), paid tribute to Goryeo for a certain period, Goryeo struggled to maintain control over nine fortresses (東北九城) within the newly conquered territory. Discontent simmered among those Jurchen tribes previously allied with Goryeo who had lost their land following Goryeós expansion. This ultimately led them to join forces with the Wanyan Tribe in resisting Goryeo. As a result, Goryeo returned the newly acquired northern territories back to the Jurchens. Freed from the immediate military threat posed by Goryeo, the Jurchens were then able to accelerate their unification efforts and ultimately challenge the hegemony of Khitan (National Institute of Korean History 2021).

A pivotal factor in Jurchens' swift ascent can be attributed to the unique governance system implemented by Aguda (阿骨打), the founder of the Jurchen Jin Empire. Under this system, private soldiers and tribal leaders enjoyed equal access to food and participated in decision-making committees, regardless of their social status (Xiong and Hammond 2019, 220). This egalitarian approach was further reinforced by Jurchen's conquest of mainland China. During their military campaigns against the Liao, the Jurchens incorporated Khitans into their army. Units called meng'an (猛安) were formed, each consisting of 1,000 Khitans, and their leaders were appointed as rulers of the newly conquered territories. This strategy proved instrumental in facilitating rapid conquest, and the Jin emerged as a formidable power in North China upon capturing the last Liao emperor in 1125.

In 1117, Khitan relinquished ownership of Boju to Goryeo under the threat of the war with Jurchen. From this, the southern part of the Amnok River came under control of Goryeo. Despite the long territorial disputes, Goryeo occupied Boju without military clashes (Kim 2012a, 160). The Jin did not respond to Goryeo’s action. Recognizing the protracted dispute between the Liao and Goryeo in the past, the Jin concentrated on the war with the Liao and did not oppose the dominance of Boju over Goryeo. It was an implicit agreement to avoid conflict with Goryeo (Kim 2012a, 155-156). After the occupation, all the officials of the Goryeo court congratulated the “restoration” that had been achieved after a century-long conflict (Goryeosa sega Yejong 12th year 3rd month). This achievement represented Goryeo’s prolonged security policy in relations with the Chinese powers in the north.

Diplomatic contacts between the Song and Goryeo progressed with the demise of Liao and the rise of Jin. When Song requested Goryeo’s aid to conquer Jurchen in 1115, chief officials in the court of Goryeo expressed their opposition to military intervention (Goryeosa jeoryo Yejong 10th year 8th month). Song sent an envoy to Goryeo in 1123 with the message saying that “the Liao’s fate came to an end” and suggested Goryeo accept Song’s investiture (Goryeosa sega 13 Injong 1st year 6th month). As Goryeo stopped using the era of Liao in 1116, Song recognized the change in Goryeo-Khitan relations and tried to ally with Goryeo (Kim 2019, 9). But Goryeo rejected this offer.

During this period, Goryeo-Jin relations changed dramatically. As mentioned above, Goryeo engaged in the war with the Jurchens in 1104 and 1107 and was able to drive them out to north and expand its territory. However, there was a burden of maintaining the new territory with Jurchen’s backlash and securing the newly constructed nine fortresses. Soon, the fortresses were abandoned in exchange of Jurchen’s oath of allegiance to Goryeo. During this period, Jurchen officially called Goryeo their “father country.” Later, Jurchen succeeded in the unification of tribes and won the war against the Khitan. In 1117, contradicting the previous oath of allegiance, Jurchen declared the Jin Empire and referred to the king of Goryeo as “younger brother.” And Jurchen Jin sent an official letter to Goryeo to readjust the bilateral relations (Goryeosa sega 15 Yejong 12th year 3rd month). The court of Goryeo expressed antipathy against this sudden change but postponed an official response.

Until 1125, Goryeo maintained a relatively assertive stance towards Jin, while Jin adopted a cautious approach (Cho 2011, 81). The fall of Khitan Liao in that same year triggered a radical shift in Jin's attitude. When Goryeo dispatched an envoy to Jin, Jin rebuked them for not acknowledging their status as a subject state and refused to accept Goryeós official written letter (Goryeosa Injong 3rd year 5th month). This served as a gesture and a form of pressure from Jin, demanding a reassessment of the Goryeo-Jin relationship. Ultimately, Goryeo decided to establish tributary relations with the Jin in 1126. According to the Goryeosa (⾼麗史), all court officials opposed this decision, but it was pushed through by the two most powerful men at the time – Yi Ja-gyeom (李資謙) and Cheok Jun-gyeong (拓俊京). One reason for this opposition may have been the court's voluntary declaration of a subordinate position even without an official request from Jin, a decision that was nonetheless welcomed by Jin (Kim 2019, 18). In 1126, Goryeo adopted the Jin era and sent an envoy to Jin with a document officially declaring Goryeo as a subject state of Jin (Jinshi Juǎn³ běnjì3 Tàizōng tiānhuì 4nián 6yuè bǐngshēnshuò).

It is noteworthy that despite the presence of conflicting political factions, Goryeo maintained a consistent foreign policy. In fact, the two most influential political figures, Yi Ja-gyeom and Cheok Jun-gyeong, who advocated for tributary relations with the Jin, were at odds with King Injong, who eventually lost power after his followers' failed assassination attempt against the two. Moreover, Cheok, a military officer who had played a significant role in the war against the Jurchens, was known for his military prowess. One might have expected him to adopt a hard-line stance, yet he demonstrated a preference for a non-violent diplomatic approach towards the rising power.

As mentioned earlier, the majority of court officials in 1126 considered the notion of serving Jin to be unthinkable. However, the king opted to follow the minority opinion of Yi and Cheok, who insisted on sending an envoy to pay their respects and express courtesy. Yi and Cheok said, “When Jin was a small country, it served Liao and our country. Yet, now Jin has rapidly risen to power and destroyed Liao and Song. It is well-governed, and its military is strong and becoming stronger day by day. Since we face a border with it, we have no choice but to serve Jin” (Goryeosa sega Injong 4th year 3rd month). This record clearly reveals the perspective of the two decision-makers who held sway over the king. They believed that Goryeo had no viable diplomatic options beyond aligning with Jin, given the rapid collapse of two major powers - Song and Liao. Just four days after this gathering, the court convened to decide whether or not the country should serve Jin. As recorded, “Jurchen, having proclaimed itself emperor, has subjected many and expanded its territories by invading Song in the south and destroying Liao in the north. Since our country borders with them, we would like to seek your counsel on the issue of whether we should dispatch envoys to maintain peace or raise troops in preparation for war” (Goryeosa sega Injong 4th year 3rd month).

From both of the above records discussing the relations with Jin, it is necessary to note that political groups in Goryeo began to take the issue of the rise of Jin seriously and shared the pressure from a possible military conflict. This recognition was understood as Jin’s “wave of the future” Jin by Goryeo, which encouraged a tendency toward bandwagoning to the rising power. Although it was recorded as a decision by two powerful leaders who were yet in the minority, it was a decision made by the state evaluating the rapidly changing international environment from Jin’s emergence as a major power in East Asia.

The prudence and consistency in Goryeo’s foreign policy can be found in later records. Yi in 1126 and Cheok in 1127 were sentenced to exile. Despite the fact that those who were known to have been the most active in establishing tributary relations with Jin from the seemingly immense opposition were expelled from power, King Injong and the court did not discuss aggressive measures in diplomatic relations with Jin. In this sense, it can be understood that the majority position of the opposition was an ostensible political gesture.

Further, Goryeo seemed to recognize that realigning relations from Liao to Jin was an inevitable reality. In September 1127, Goryeo sent an envoy to congratulate the emperor’s birthday and received an official letter from the emperor. The emperor of Jin said,

“Initially, Song requested the return of Yu and Yan (幽燕) and secretly sent an envoy to the sea route to have friendship with neighboring countries. Our last emperor took pity on the earnest request and immediately granted it. However, they did not know that they had to keep a firm oath, and instead accepted those who ran away and created resentment. Zhao Hwan (Qinzong of the Song, 欽宗) succeeded the throne and repeated the actions of Zhao Ji (Huizong of the Song, 徽宗). … In the end, he incurred the wrath of God and people, and heaven and earth did not tolerate it. When their lair was overthrown in just one expedition, they were unable to protect the royal shrine and the father and son became captive. As the discord between each other deepened, there was a change of dynasty.” (Goryeosa sega Injong 5th year 9th month)

In response to this, King Injong again wrote a letter saying, “The extraordinary victory and the special grace rarely seen in the world are truly unheard of for a long time, and the whole country reveres and admires them.” (Goryeosa sega Injong 5th year 10th month) In a limited policy choice, Goryeo’s foreign policy with Jin should be understood as a practical approach by policy makers, rather than an arbitrary decision of individuals in power (Kim 2019, 26).

When a Goryeo envoy to Song came back due to the Jin’s occupation of the capital city of Song in 1127, misinformation from the border was reported to the court of Goryeo that the Song was winning against Jin. Nevertheless, the court suggested that it should not build up military forces against Jin (Goryeosa jeoryo Injong 5th year 5th month). The overall flow of the foreign policy of Goryeo was to retain the trend of a careful diplomatic approach and avoid military conflict with Jin. It was Goryeo’s perception of interest to avoid military clashes with the rising power by bandwagoning to Jin through the establishment of diplomatic relations.

Shortly after the establishment of political ties between the two states in September 1126, Taizong of Jin raised the issue of ownership of Boju. Specifying the standards for commuting between the two states, Jin demanded the repatriation of Jurchen people who entered Goryeo. The Jin emphasized the sending of a written oath (誓表), arguing that Goryeo acquired Boju through the empire’s concession. In addition, it further suggested not to raise objections to Jurchens who cross the border for farming. Part of the argument is that Goryeo only occupied the city of Boju but the boundaries along the Amnok River had not been established. In response, Goryeo sent an envoy to convey its position to Jin as follows,

“Go Baek-suk (高伯淑) came and secretly conveyed the will of the emperor, saying he will vest Boju in Goryeo and will not claim it again. I think that the mainland of Goguryeo (高句麗) was centered on Yosan (遼山), and the old site of Pyongyang (平壤) was bounded by the Amnok River, which changed several times. Then, in our ancestors, the Liao came to the north, occupied it, and invaded the land of Samhan (三韓). Although we sought protection, the old land was not returned. … During the time of my father’s reign, Saeulha (沙乙河), an official of the Liao at the border, came, delivered the emperor’s edict, and said Boju is originally the land of Goryeo, so it is right for the state to restore the land. Accordingly, the late king repaired the fortress and ponds and moved the people to the city. At that time, even though our country had not yet been subordinated to your country, the late emperor sent a decree to show favor to the neighbor by granting the old land. This small land on the eastern seashore was originally a border area of our country, but was divested by the Khitan. As we already received favor from the late emperor, and now you are giving a special benefit by subjugating to our country. How did this happen? It is thanks to the emperor’s special grace.” (Goryeosa sega Injong 4th year 12th month)

The letter above demonstrates Goryeós acknowledgment of the northern territory around Boju and the diplomatic strategy it employed in its interactions with Jin. Firstly, Goryeo recognized Goguryeo as its ancestral homeland and asserted its sovereignty over the old territory based on this perception, despite facing challenges in securing the land due to ongoing conflict with Liao. Secondly, the territorial issue between Goryeo and Liao centered on Boju, and Goryeo consistently pursued the acquisition of Boju by asserting its sovereignty over the region. Thirdly, the territorial issue surrounding Boju resurfaced in the diplomatic relations between Goryeo and Jin, highlighting the significance of Boju in determining the border between the two states. At that time, Goryeós primary objective in its diplomatic dealings with Jin was to secure the confirmation of Boju as part of its territory. These points suggest that the occupation and recognition of Boju under Goryeós territorial basis were the primary benefits Goryeo sought in establishing tributary relations with the Jin. Ultimately, Goryeo officially submitted a written oath to the Jin in exchange for the approval of occupation of Boju.

This time period, immediately after the fall of the Liao and Northern Song, is significant in terms of international relations. Raising the question of Boju by the Jin was rather the purpose of making the diplomatic relations clear and means for requesting a written oath than territorial conflict (Park 2011, 31). The Jin sought its interest by seeking formalizing an international order through the foundation of diplomatic relations with the Goryeo Dynasty. The empire first rejected communication with Goryeo that did not officially declare the position of a weaker state (servant) but immediately formalized the relations with Goryeo when it sent an official document calling itself as a servant, which symbolized a recognition of Jin as a major power.

For Goryeo, the establishment of a tributary relations was not a loss. During the time of the demise of the two empires, Liao and Northern Song, Goryeo participated in the new international order set by Jin in order to benefit from it. By acknowledging Jin as an older brother, the younger gained a northern land so that a century-old dispute was finally resolved without a war or significant cost. In this sense, the issue of Boju was an agreement on the pursuit of different national interests between the two states in the newly formed international system.

This diplomatic flow was different from the one in Goryeo-Khitan relations that was mostly in tension as Goryeo sought national interest in the firm control of Boju through international approval of its sovereignty for the resolution of security concerns in the northern border areas, which had continued since 993. For Jin, Boju was not a critical strategic spot since the area was no more than the border neighboring Goryeo. It was strategically more important to the Liao when it had to face with both Goryeo and the Jurchens, while Jin had no reason to maintain tensions with Goryeo for the area without the presence of Liao. Rather, Jin had the priority of preventing Goryeo from joining in adversarial rival coalition possibly with Song. On the other hand, Goryeo was finally able to end the long-standing security unrest through the acquiring Boju and demarcating the border along the Amnok River in exchange of declaring itself as the servant, recognizing Jin as its partner in the international system.

Goryeo also maintained its stance to exclude military cooperation with the Song. Northern Song allied with Jin to destroy its rival Khitan but soon had to offer a tribute to Jin more than it had to do to Khitan in the past. In 1126, Song sent an envoy to Goryeo to request military assistance amid the threat of the Jurchen. In the letter brought by the envoy, the urgency and bewilderment were apparent; Song highlighted “fidelity” and offered a Song-Goryeo joint forces to balance against Jin (Goryeosa sega Injong 4th year 7th month). Goryeo responded that Jin destroyed Liao because “Khitan was abandoned by Heaven” and rejected the proposal, saying that Goryeo was not in a situation where it could raise military forces against Jin in a short period of time due to insufficient supplies and food (Goryeosa sega Injong 4th year 7th month).

Evidently, Goryeo’s decision turned out to be right. Northern Song collapsed as the capital Kaifeng (開封) was captured by the Jin in 1127, and Southern Song was founded along the Yangtze River. During this period, Jin sent an envoy to Goryeo to notify the destruction of Song and capturing the emperor Huizong (徽宗) and Qinzong (欽宗). Goryeo congratulated the victory of Jin by referring it as “peace under Heaven” and sent a message stating that it promised to be loyal to and serve Jin (Goryeosa sega Injong 5th year 10th month). Southern Song again sent envoys to Goryeo to ask for a road to attack Jin at its back, but Goryeo declared that it would not intervene in the Song-Jin confrontation (Song shi juan 487 liezhuan 246 waiguo 3 Gaoli).

The emergence of a new power that replaced the international order and even had bigger influence by driving Song into the area below the Yangtze River motivated Goryeo to pursue its interest in the new setting. Considering that engaging a political affair with Southern song would be a burden, Goryeo in 1128 also refused to approve the use of its road for the repatriation of the two emperors captured by Jin (Goryeosa sega Injong 6th year 6th month). Goryeo explained that the Jurchen had become too powerful, forcing Goryeo to declare itself a subject, and the empire had stationed troops near the border while being aware of Goryeo-Song relations (Goryeosa sega Injong 6th year 6th month).

Still, Southern Song did not give up and the envoy stayed in the capital to have an approval. Goryeo squarely confronted Song’s demand at this time by saying that the Jurchens is also good at naval warfare, so the war can occur both at the land and sea (Goryeosa sega Injong 6th year 8th month). In the court of Southern Song, Zhu Shengfei (朱勝非), the Right Minister of Shangxi (尚書右丞), said, “Goryeo neighbors on Jin and is separated from us by the sea, so their interests are very clear. Even though we treated Goryeo too generously in the past, how can we demand repayment now?” (Songshi juǎn 487 lièzhuàn 246 wàiguó 3 gāolí sònggāozōng jiàn yán 2 nián 10 yu) This demonstrates that Goryeo’s foreign policy choice was understood even in Southern Song.

Like this, amid the rise of Jin, Goryeo saw that bandwagoning to Jin was more in line with pursuing its national interest than balancing against Jin through alignment with Song. As time passed, this tendency became clearer with its evaluation of the power imbalance between the two empires.

For Jin, the readjustment of diplomatic relations with Goryeo was the beginning of a new international order under its leadership. In 1142, Jin carried out investitures of Western Xia, Southern Song and Goryeo, symbolizing the consolidation of international relations in East Asia under Jin hegemony (Park 2011, 28). At this juncture, Goryeo officially formalized its tributary relationship with Jin, abandoning its previous alliance with Southern Song to maintain a balance against Jin's growing power. This paper argues that Goryeós decision to bandwagon with Jin was a strategic choice driven by interest, as the decline of Khitan and the rise of the Jurchens compelled the dynasty to reassess its priorities and seek more than mere survival.

For Goryeo, securing the border along the southern fringes of the Amnok River was a paramount objective that had been pursued for centuries amidst power struggles and shifting dynamics of the international order. During the Liao-Jin conflict, Goryeo not only maintained a cautious stance to assess the potential impact on the statés future but also actively sought opportunities to advance its national interests. The occupation and firm control of Boju served both to resolve the century-old territorial dispute and address security concerns, ultimately prompting Goryeo to embrace tributary relations with Jin. Unlike Liao, which faced both Goryeo and the Jurchens along the Amnok River border, Jin, upon relinquishing Boju and recognizing it as Goryeós territory, gained a measure of security stability, enabling it to focus its expansionist ambitions on mainland China.

The “mortifying” bandwagoning with Jin marked a significant achievement for Goryeo, addressing the issues of territorial expansion, northern border demarcation, and reduced military confrontation. In contrast to the fall of the two empires in China, Goryeo successfully navigated the potential for military conflict with Jin and emerged as a core member of the Jin-led international order, which persisted for over a century. Furthermore, the acquisition of Boju was widely applauded for stabilizing the territory, a prospect that seemed unlikely under the Khitan-led international structure. Consequently, Goryeós bandwagoning with Jin represented a strategic choice in its foreign policy, effectively resolving security concerns and ushering in a century of peace until the rise of Mongolia in the 13th century.