The Limits of the Japan-South Korea Military Relationship
Image Credit: Cheong Wa Dae

The Limits of the Japan-South Korea Military Relationship


The Republic of Korea (ROK) and Japan have yet to implement a formal military alliance with each other. Instead, they manage the bulk of what little military cooperation they exercise through their triangular relationship with the United States.

Their lack of a formal military alliance is an anomaly in the world given their geographic and cultural closeness and shared threats. Japan and South Korea’s inability to formalize a bilateral military relationship is the result of too heavy a focus on past grievances, versus focus on contemporary and future threats. This situation has been enabled by overreliance on the United States as the guarantor of security Northeast Asia. But perhaps more interesting to consider as the Cold War fades further into the past, if Japan does not make a serious effort to secure a stronger relationship with South Korea, it is possible that it could lose the ROK to China, given the three countries’ historical relationships.

South Korea-Japan Lack of Bilateral Military Alliance

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The ROK and Japan’s lack of military relationship over the past decades is strange when viewed through the lens of realist theory, given their overlapping security interests and mutual threats, e.g., the Democratic People’s Republic of Korea (DPRK). As Sheryn Lee argues, it is an anomaly from a constructivist perspective as well, given their shared culture and democratic governments. In fact, as Jiun Bang shows through quantifiable data (based on factors such as geographic proximity, cultural similarity, shared history, and shared threats), the ROK and Japan’s lack of military cooperation is outside of the norm when compared to the level of cooperation typical with such a convergence of factors between other countries.

On the surface, the lack of military cooperation looks to be the result of unresolved animosity from the colonial period. One could look to a combination of the lack of sincere repentance from Japan and the Korean people holding historical grudges as the reasons the two countries are continuously thwarted in their efforts to strengthen military cooperation. But this is not a sufficient explanation. No pair of countries can afford to let emotions govern their security relationships in the face of real threats. Other countries with histories of conflict have been able to show more cooperation. France and the United Kingdom after centuries of warfare, the United Kingdom and the United States after the colonial period and wars of the 18th and 19th centuries, and France and Germany after two world wars are examples of countries that put past differences behind them and demonstrated significant military cooperation.

It is possible that there is something different in the psyche of South Korea and Japan, or perhaps in Asian countries in general, when compared to the West. Possibly, as Acharya and Buzan suggest, Western international relations (IR) theories do not always apply to Asia. While there may be some truth to these two points, a better explanation can follow from examining the circumstances surrounding the times when Japan and South Korea did feel compelled to cooperate.

Historical Patterns of South Korea-Japan Military Cooperation

Victor Cha analyzed South Korea-Japan military cooperation best in his study examining the Cold War and the 1990s. He argued that security cooperation happened when the perceived threat was severe enough. Jiun Bang further backs this up with her analysis including cases and data as recently as 2010, showing the security relationship to be ad hoc and threat based. What is particularly interesting about Cha’s analysis, however, is he concludes that the key determining factor is not the threat itself, but South Korea and Japan’s perception of the United States’ ability and willingness to counter the threat.

Evidence from the Cold War era supports this. As Cha shows, South Korea-Japan military cooperation spiked after the U.S. withdrawal from Vietnam and the ensuing Nixon Doctrine, a time of perceived reduction in the U.S. commitment to defend Asia. Cooperation spiked again when President Jimmy Carter announced his plan to withdraw forces from Korea. In fact, some argue that the ROK-Japan 1965 Treaty on Basic Relations came about at a time when the United States seemed to be losing the Cold War.

Knowing that the United States is still there acting as a deterrent may also account for why in more recent years, even while presenting a unified front in statements responding to DPRK saber rattling, South Korea and Japan are still unable to move forward on bilateral military agreements. Seoul canceled the planned signing of two agreements with Japan, the General Security of Military Information Agreement (GSOMIA) and the Acquisition and Cross-Servicing Agreement (ACSA), in 2012. Both agreements have been shelved ever since. This is an example of the two countries allowing popular negative sentiment over history to detract from their military cooperation. No counties so close to a nuclear armed, unpredictable enemy like North Korea could afford to allow emotions over the past to interfere with their cooperation on national security if not for the guaranteed protection from a third party.

Therefore, it is the United States that has enabled Japan and South Korea to avoid formalized military alliance. They have the luxury of allowing emotions to continue to play such a powerful role in their relationship precisely because Washington has been the primary guarantor of their security since the end of World War II. This is ironic as the United States is the strongest advocate for South Korea and Japan to strengthen their military cooperation.

Future Cooperation?

It should follow then that if U.S. strength in the region were to wane in the coming years, South Korea and Japan should find themselves drawing more closely together. In fact, despite President Barack Obama’s “pivot to Asia,” it is possible that U.S. military dominance in the region could weaken in the near future. U.S. strength will no doubt decline in relative terms as China’s strength grows. Additionally, Washington may draw down its military presence deliberately if isolationist feelings take hold after these long years of costly and unpopular U.S. interventionism abroad.

If U.S. military dominance does in fact weaken, Japan and South Korea might draw together, as they did during the 20th century at times of perceived U.S. weakening. This assumes, however, that the threats are perceived the same way by both countries. But as Sheryn Lee points out, the assumption that South Korea and Japan are destined to eventually formalize their military cooperation is misplaced. There is no guarantee that the current alignment structure in Northeast Asia a permanent fixture absent sustained U.S. encouragement. Cheol Hee Park examined this and concluded that a withdrawal of the United States as the mediator and encouraging force in South Korea-Japan relations would result in the two balancing against each other, rather than aligning to balance against China.

Many still see the alignments of Northeast Asia as it was during the Cold War. But the end of the Cold War is now a quarter of a century in the past. While Pyongyang is no doubt a menace to both Seoul and Tokyo, communism is no longer the monolithic threat. More recent studies suggest South Korea does not perceive the People’s Republic of China as threatening to the same degree that Japan does.

Korea’s Traditional Place Next to China

In the coming years, it is not unreasonable to imagine that South Korea may find itself aligning more closely with China than Japan. This becomes increasingly conceivable if one considers the deeper historical context beyond just that of past 60 years. China before 1949 was not a traditional enemy of Korea. On the other hand, scholars have described Japan as having for centuries been “one of Korea’s most dreaded foes.” In fact, Japan has been the traditional enemy of both Korea and China. Conversely, Korea existed for centuries as a tributary kingdom within the Chinese dynastic sphere. As China rises, Japan re-militarizes, and U.S. influence declines in relative terms, Korea opting for closer relations with China over Japan could be viewed as a return to its stable Choson past.

Beyond the pre-Cold War historical relationship between Korea, China, and Japan, there are contemporary pragmatic reasons why Korea could shift away from Japan and toward China. First, unlike Japan and most of the rest of Asia, Korea does not have significant territorial disputes with China. The Socotra/Suyan Rock dispute — a dispute over maritime boundaries rather than territory — in the East China Sea between South Korea and China is of practically no concern when compared to the Senkaku/ Diaoyu dispute between Japan and China or any of China’s disputes in the South China Sea. Meanwhile, South Korea’s most significant territorial dispute, over the Dokdo/Takeshima islands, is with Japan.

Additionally, while South Korea may take issue with China on human rights and democracy related issues, this would not necessarily prevent security relations between the two. Regardless of what China does domestically, its policy of not interfering in other countries’ domestic affairs could make China seem non-threatening to Korea. This is all the more salient when considering the fact that public opinion in South Korea is distrusting of Japan’s re-militarization. This increases the likelihood that Japan, not China, could become the primary perceived threat in the Northeast Asia region (aside from North Korea).

Most significantly, however, is the possibility that China could prove a more useful ally in managing North Korea. There are several reasons for this. First, as China shares a border with the DPRK, it is a more significant and permanent stakeholder than the United States and Japan could ever be. Secondly, China can wield greater influence over North Korea as its primary benefactor, while U.S. and Japanese efforts have resulted only in further antagonizing Pyongyang. If South Korea and China ever presented a unified front in their dealings with North Korea, a negotiated solution to the decades long separation of the peninsula could be possible. The key would be that China would no longer have to fear a U.S.-Japan aligned Korean government being the result of a reunified peninsula. This has already been suggested as a motivating factor in South  Korea’s perceived neutrality in the increasingly contentious East and South China Sea disputes. A South Korea-China alliance could become an increasingly desirable possibility as the ever more reckless Kim regime becomes more of a liability to China.


Given the continuing strength of the South Korea-U.S. partnership, a prediction that Korea will abandon the United States and Japan in the future to fully join the China camp is premature. Instead, the point is that a bilateral Korea–China relationship that is stronger than Korea–Japan ties is not completely far-fetched, especially if the United States becomes less of an influencing factor in the region. For decades Washington assumed that South Korea and Japan were destined to be great allies and secure the West-aligned interests in Northeast Asia. All that was required was for Korea to “get over” the past, which the United States assumed the ROK would do eventually. Japan, likewise was able to continue to avoid serious repentance toward Korea over its colonial relationship with the peninsula due to the realities of the Cold War security situation.

Yet, Japan and the United States may have taken Korea for granted. It is worth reminding both Tokyo and Washington that for centuries China was Korea’s only ally, before the Sino-Japanese war brought the situation to an end. As the Cold War fades further into the past, there is no guarantee that South Korea and Japan will eventually become strong bilateral military allies independent of the U.S. triangle. As China grows stronger and Japan seeks to reemerge as a regional military power, Japan may need to take the initiative to win Seoul over to its side if it wishes to balance against China. The onus being on Japan is also in line with the historical past. As former Japanese Prime Minister Nobusuke Kishi famously observed, it has always been Japan’s responsibility to ensure the security of the Korean Peninsula, as it is vital to the security of Japan. It was with this in mind that he encouraged Hayato Ikeda’s administration to do whatever was necessary to normalize relations with South Korea in the 1960s.

It takes two sides to come together for an agreement. But with South Korea’s options to play China, Japan, and the United States against each other, the burden to strengthen the ROK–Japan relationship falls on Tokyo In this situation, concessions from Japan may no longer be out of the question. Relinquishing its claims to Dokdo/Takeshima, addressing the trade imbalance, or simply making one final apology that is satisfactory to Koreans may be small prices to pay if Japan sincerely tries to make a push to keep Korea on Japan’s side.

Peter Murphy is a U.S. Army Civil Affairs officer and a Master’s Candidate in Global Affairs and Policy at Yonsei Graduate School of International Studies in Seoul. He received his Bachelor’s degree in History from the University of Michigan and a Master of International Relations degree from Bond University in Australia. The views expressed in this article are his own.

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