Author: Reuben F. Johnson

A Complicated Trilateral Alliance

In the final year of World War I, The Supreme Allied Commander was the French Marshal Ferdinand Foch, who is generally considered as the military leader most responsible for the Allied victory in the conflict. He was a disciple of the Napoleon school of military thought, was sometimes compared to the famous French military genius and upon his death was buried next to Napoleon himself at Les Invalides in Paris.

Therefore, it is somewhat surprising to learn what he said about the one-time French emperor after experiencing first-hand the challenges of commanding the entire Allied war effort. Keeping all its many partners in line, on message and content with their roles in the hostilities proved to be the most difficult of all the aspects of the Commander-in-Chief’s job.

Foch’s comment was that having been the head of a grand coalition of nations he had consequently lost much of the respect he once had held for Napoleon. A military and political leader with near-dictatorial powers is empowered to issue orders that would never be rescinded or countermanded – not even questioned – and has no fear of being thrust into a contentious environment where each one of the alliance members gets a vote.

The act of holding together an alliance of democratic states which have their own political leadership, and their own domestic priorities will always be an infinitely more challenging proposition than the commander who is a dictator. In the case of the Republic of Korea (ROK) and its two major partner nations in Asia – the US and Japan – there are no end of complications despite there being only three members of this “club.” 

The three nations do share common security and defence interests, but there are also numerous non-military issues – trade, economic stability, technological development, freedom of navigation, etc. – that they all support and cooperate to the degree possible to promote. But like Marshal Foch discovered, holding together an alliance of nations that have a common strategic objective is by no means a smooth road of travel all the time. The alliance will nonetheless still be fraught with any number of challenges.

In the best of times in the domestic politics of one or more of the three, no matter the security situation or potential conflict scenarios, relations between the US, the Republic of Korea (ROK) and Japan represent what is probably one of the more complicated of any trilateral alliance of modern times. This is despite of the numerous objectives and values they hold in common.

In the aftermath of a very challenging year in ROK politics the question that is being asked is if there is the possibility of any slowdowns, disruptions or other alterations in the functioning of this trilateral alliance. The single defining event or watershed moment is this past June’s presidential election in Seoul and the events leading up to it. This crisis of course began initially with President Yoon Suk Yeol’s imposition of martial law on 3 December 2024. This set in motion numerous reactions that caused significant concerns in Japan, as well as globally, with the main question on everyone’s minds being whether or not there had been a breakdown in the political stability of the ROK.

As a recent analysis highlighted, “South Korean President Yoon Suk Yeol’s imposition of martial law on 3 December 2024, precipitated a train of events that have raised grave concerns in Japan and globally about political stability in Korea.” By the time the presidential election took place this crisis had been extended for more than six months. “The lack of both domestic and high-level diplomatic leadership could not have come at a worse time, given the return of Donald Trump to the American presidency and his administration’s subsequent imposition of tariffs on the highly export-dependent nation,” continued the same assessment.

What happened during this period speaks volumes about why this trilateral alliance continues to exist and even strengthens over time.

In this six-month period up to the election Japan was closely monitoring events, taking steps to promote a return to normalcy during this period of instability and in the absence of stable South Korean leadership. The Japanese government was providing diplomatic support to the ROK and coordinated closely with the government institutions in Seoul. Tokyo and Seoul also did not hesitate to continue advocating closer Japan-ROK and US-ROK-Japan cooperation during this period.

The “lessons learned” from this experience is that it shines a spotlight on the difference between dictatorships and democracies. Dictatorships are brittle. Democracies are resilient. Dictatorships are usually the nation-states that start wars. Democracies rarely – if ever – go to war with one another. Despite the complications that exist in this trilateral alliance, the individual members will take all measures possible to ensure that it stays together and to maintain their resiliency.

 

Elections and the Three Major Factors 

An early 2024 assessments of ROK-US relations spelled out how the relationship between the two nations had remained in place after more than 70 years. The author lists out three factors that impact on the strength of an alliance. Each one of the factors can have influence on one or both of the others. If any of the three conditions that were initially present and led to the formation of an alliance alter measurably, that alliance is likely to experience changes that eventually affect the longevity of the alliance.

The changes that the three conditions of alliance formation undergo respectively are:

1) External Threats: Member states of an alliance may develop divergent threat perceptions and continue to believe in the necessity of the alliance due to changes in international relations. 

2) Capability: Changes in the capabilities of allied states can affect rationales for the alliance itself. An alliance member whose capabilities have increased may seek to terminate the alliance and instead increase military spending for self-defense of their own nation rather than for the collective security of the alliance members. This is particularly the case in asymmetric alliances, where the weaker parties are vulnerable to interference in domestic politics and foreign policy from the stronger parties. That vulnerability is naturally due to the power differential between them. Any increases in the weaker parties’ capabilities may lead to terminating the alliances in order for one or more of the alliance members to gain autonomy. 

3) Domestic Politics: Changes in domestic politics, which are normally associated with democratisation, can affect alliance cohesion. If newly elected leaders in democratising countries see the dynamics of the alliance differently from their predecessors they can become less committed to the alliance.

Viewed through the prism of these three factors, the alliance of the ROK, the US and Japan is one of the more stable and robust of its kind in the world. In defence and national security affairs the three nations are increasingly united. They share the interests and objective of maintaining peace and stability in the region in general and on the Korean peninsula and in the Taiwan Strait in particular. The ROK shares a list of common concerns and potential threats to its security that in numerous instances overlap with those of the US and Japan.

These security issues are not the only common denominator between the ROK and its two allies either. Cooperation in defence and foreign policy activities constitute a robust and strategically significant agenda upon which all three can usually agree. But there are other shared values between the ROK and its allies that make this a broad-spectrum trilateral arrangement that is not narrowly confined to the defence sphere alone.

That of course means that there are items on the domestic and non-defence agenda that can be a mixed bag at the moment, depending on what the focus of any particular inquiry might be. It is no secret that the ROK has been through a prolonged period of domestic unrest in 2025. But now that the presidential election has taken place and the political environment has stabilised, what is the likely road forward from here. Specifically, how is the outcome of this election likely to affect this trilateral relationship and would there be any change in the dynamics of defence partnerships and cooperation between the three.

The unhappy truth is that the new ROK presidential administration could very well take a course that ends up being a retrenchment of the progress made in the past four years in strengthening the trilateral alliance.

With new president Lee Jae Myung, who is viewed as a progressive from the Democratic Party, replacing his impeached predecessor, Yoon Suk Yeol, there will be immediate action items that will have to be addressed. One of those is that there will be a reformulation of foreign policy that is consistent with the Democratic Party’s stated positions on various issues. This is not due solely to the aftershocks of the impeachment and the six months of uncertainty as to who would be running the country. It is also the changes in Washington in foreign affairs under US President Donald Trump. Not the least of these is Trump’s assertive tariff agenda, which the new ROK president will have to cope with while simultaneously addressing traditional and perennial domestic economic and social issues.

The ROK is one of the most impressive, energetic, productive and technologically advanced nations in the region – as well as in the world. As one group of Asian policy analysts write, the country is a “rich, democratic, globally integrated middle power [and] has all it needs to punch above its weight in international affairs. But despite strong national capacities, a highly developed and globally connected economy, a significant overseas investment footprint and cutting-edge technological capabilities, Seoul often appears more reactive than agenda-setting in international and Asian affairs.”

This lack of more aggressive activity in foreign affairs is surprising given the manner in which the ROK defence industrial sector operates in foreign markets. Firms like Korean Aerospace Industries (KAI) and Hanwha are some of the most aggressive and pace setting of any other firms of their kind in any other nations. Two years ago, the Korean aerospace firm were already talking about their long-term corporate strategic plan called “Global KAI 2050 — Beyond Aerospace” that has a goal of making the company the seventh-largest aerospace firm in the world and to expand their export client list to the point where they are increasingly less dependent upon the ROK government for the majority of its sales.

However, the same Australian National University analysts referenced above assess that “bad luck with history and geography is partly to blame. The enduring threat from North Korea has engendered a security dependence on the United States, while unresolved historical grievances with Japan complicate the pressing agendas for cooperation with Tokyo.”

Another element is that South Korea’s international policy initiatives are heavily influenced by changes in domestic political dynamics. Each new presidential administration often ends up disassembling or even reversing the significant policy changes or any specific new relationship-building accomplishments of its immediate predecessor. This is a fairly important issue to watch closely as the new administration begins to formulate its own agenda and re-visit all the policy initiatives it inherited from Yoon’s tenure in office.

There is thus more than just a remote possibility that this traditional tendency of new administrations to tinker with foreign policy could end up “turning back the clock” on the progress made in ROK-Japan relations. There were agreements between the two nations reached during the Biden Administration that were so far-reaching that they have been described as a “reproachment.” Experienced South Korea-watchers literally warned that the optimism about relations between the ROK and Japan amid the premature euphoria that marked the strengthening of Japan–South Korea during the Biden administration. Their warning was that a new administration might decide to take a different course – including a course backwards – for no other reason than “because they can.” 

Yoon is credited as being instrumental in organising the August 2023 ROK-Japan-US trilateral summit at Camp David. This summit most likely would never have happened in the first place if Yoon had not made a major effort in seeking a reconciliation with Japan, with which Seoul has a troubled history. The summit did not produce an agreement for a formal, official military alliance, but the language of the agreements reached bear significant similarities with the principle of Article 5 of the NATO charter. The language of “an attack against one is an attack against all” was almost duplicated, only with the word “attack” being replaced with the “threat.” Suggestions were even made that the new trilateral security partnership might be of greater significance than the tri-party AUKUS pact.

Yoon’s foreign policy was one that placed a primacy on democratic values and practices. He pushed for a formalised and robust security arrangement with Japan as the country was and would continue to be, in his words, “a partner sharing universal values.” Yoon’s administration was also more vocal than his predecessors in condemnation of the Democratic People’s Republic of Korea’s (DPRK) human rights record and the coerced repatriation of North Korean escapees by the People’s Republic of China (PRC).

His position on these points is one of the factors that motivated the reinforcing of ties between Japan and South Korea – and in conjunction with both nations’ alliances with the United States. The summit did not produce a collective security arrangement, but the final agreement contains a two-paragraph “commitment to consult” on how the nations would collectively respond to “regional challenges, provocations, and threats affecting our collective interests and security.” The fact that the two Asian nations signed off on a document with this kind of language has been described as a “stunning achievement.”

 

Security Threats in Detail

It is sincerely hoped by many that Lee’s new administration will continue to abide by and operate under the conditions of this agreement, as there is no shortage of security dilemmas in the region. For its part, Tokyo has stated its continued commitment to a solid alliance with the ROK. On April 4, Japanese Prime Minister Ishiba Shigeru was affirmed that “this year marks the sixtieth anniversary of the restoration of ROK-Japan relations. Regardless of the circumstances, we are going to make close cooperation between Japan and South Korea one of our top priorities.”

Briefly, three of the major threats to a secure, peaceful and stable region that affect all three partners are:

• An aggressively expansionist People’s Republic of China (PRC). The list of actions that Beijing has engaged in as of late demonstrate that the Chinese Communist Party (CCP) and its military arm, the People’s Liberation Army (PLA), are committed to building an increasingly larger presence of its armed forces in the region. They are also even more committed than ever to upending the rules-based world international order, which includes the expropriation of the territory of other nations in the region.
• A nuclear-armed Democratic People’s Republic of Korea (DPRK) is another threat which continues to exist and – some would say – becomes more worrisome all the time. The regime in Pyongyang is almost single-minded in its determination to never give up and to build on its nuclear capability. This means continuing to expand the size of its nuclear arsenal. Its armed forces are also based on largely moderately-capable to almost obsolete fleets of military hardware. As an example, the Korean People’s Army’s most modern tactical combat aircraft are some of the oldest variants of the Mikoyan MiG-29 fighter still flying. Therefore, for the Kim Jong-un regime, nuclear power is the fulcrum that is used to leverage the offensive military power of the nation to a degree that a nation with a more modern conventional capacity would not.
• The first two threats to the security of the ROK and its allies have been present and have increased gradually over past decades. But a third threat that has emerged in the past few years is the prospects for an increasingly unstable Russian Far East region. This latter phenomenon is no small issue. The Russian Far East not only borders on both the DPRK and the PRC and with all of the illicit trade that takes place, but it has more recently been the scene of demonstrations protesting what the residents see as the excesses of Moscow’s rule.

That discontent is fuelled by the economic growth in the region now measured as almost non-existent. Recent forecasts from the Russian Central Bank present a very sober picture for those in Moscow attempting to prevent further deterioration of federal authority in the Far Eastern region. Economic growth barely registering is largely a product of accumulating cracks and disruptions in Russia’s economy, which are now exacerbated by more than three years of war in Ukraine.

In the course of this three-and-a-half year-long war, Ukraine has not just fought a much larger Russian military to a standstill. Kyiv has additionally imposed a price on Putin for maintaining a high op-tempo of military operations that has had near catastrophic effects on the Russian economy. In turn, those economic ripple effects are now impacting Moscow’s relations with its allied partners, particularly the PRC.

Russia is increasingly dependent upon Beijing’s support for the war in the form of numerous production inputs and components. These are necessary for manufacturing weapon systems as Russian defence enterprises are constrained by Western sanctions, as well as a general international ostracism that discourages many nations from conducting any business with Moscow.

To conclude this latter point, there are forecasts by analysts with years of experience in watching the region who predict what they call the “dePutinisation of Russia”. A set of developments leading to the dissolution of the current Russian state and the Putin system evolving into a different regime once Russian President Vladimir Putin himself is no longer in power. But any such collapse in the Putin system is not likely to be peaceful in character. There are any number of scenarios that would result in security issues for all three of the trilateral alliance members.

It should be added that the collapse of the Russian state leading to the end of the Putin state apparatus is not an outcome about which there is universal agreement. The head of Ukraine’s Main Intelligence Directorate (GUR) of the Armed Forces, General Kyrylo Budanov, has stated very recently that he expects very little to change in Russia’s policies and external aggression should Putin leave power and/or his system of governance implode.

“Their system is fairly robust and stress-resistant,” he explained. “The departure of Russia’s current leader won’t change anything. They have built a system in which any successor will, at the very least, remain within the same paradigm.” He added that Russia’s power structure is fully consolidated, and any future successor to Putin is unlikely to bring about any significant changes.

“A whole generation of people has grown up in Russia who were born and have lived under President Putin — and many have already died for him. They can’t imagine any other reality. Unfortunately, the system there is quite entrenched,” Budanov stated.

A final complication is that the defence posture of all three nations is affected by the potential threat of the PRC taking military action against the Republic of China (ROC). Planning and coordination with the ROK by its two major allies – the US and Japan – will depend considerably by how the US Donald Trump Administration formulates its long-term plan of action in the event of a Mainland invasion of the ROC.

This laundry list of security threats affects the three allied nations in different aspects but ultimately addressing them requires a unified and coordinated approach. All three must agree upon a common set of objectives and the means to achieve them. Military planning is, however, one aspect in which the US and Japan should coordinate and broaden their cooperative planning and activities.

 

Conclusions

The ROK-Japan–US trilateral alliance matters for strategic reasons. It allows the US and its Indo-Pacific partners to confer on regional challenges, cooperatively develop responses to provocations and – most importantly – to those in Beijing, Moscow and Pyongyang who are watching the alliance sends a clear, unambiguous signal of the cohesion between these three partner nations. 

There is always “room for improvement” as they say. There still exist numerous areas in which it would bolster the alliance to build more robust deterrence capabilities and bolster collective defence integration against these rising threats from the PRC, the DPRK and Russia. But developing these additional structures and expanding this kind of trilateral cooperation requires, writes one analysis of the alliance quiet, painstaking and consistent diplomacy.”

It is that need for consistent diplomacy that causes some increasing concerns. One worry that has been voiced in this matter by more than one analyst is that the outlook and orientation of the current US administration with regard to diplomacy requires “constant maintenance.” This is due to Trump almost always looking upon foreign policy as a transactional proposition. His approach to diplomacy and alliances is to use measures of merit that are a product of an “Art of the Deal” perspective. This creates policies and initiatives that emphasise potential short-term gain, but not the type of long-term strategic value that is critical to this alliance.

The personnel, the organisation, the tendency to emphasise a focus on “the payoff for America” creates an administration that is not conducive to maintaining the necessary diplomatic momentum. It does not place a high value on continuing the frequency and intensity level of the engagement that has created the progress in strengthening the alliance to date.

One can make the argument that what has kept the US continuing to support Ukraine militarily to the level it does today is a unique combination of individuals and other factors. One is the skill of the recently-named NATO Secretary General Mark Rutte at keeping Trump on track, making sure he the American president is pleased with the commitments of the European-nation alliance members to higher levels of defence spending. He then created this unique arrangement in which the US “sells” weapons to our European allies, who then turn them over to Ukraine. This fits the “payoff for America” objective that Trump wants to see at the end of every foreign policy initiative.

Another factor is the skill and dedication – despite no small level of frustration at times I am told – by Trump’s special envoy for Ukraine and Russia, retired Lt. Gen. Keith Kellogg. He has been instrumental at critical moments in passing the correct messages from the Europeans at the most critical moment to the US president. 

Then there is the motivation of Trump who wants to best Putin in negotiations and at the same time produce an agreement that would end the hostilities. Playing a role as well is Trump’s motivation that by brokering peaceful agreements between protagonists like Armenia and Azerbaijan and then adding bringing the conflict in Ukraine to an end could win him the coveted Nobel Peace Prize. 

A parallel universe of personalities, skilled interlocutors, and personnel as steeped in the potential conflicts in Asia as Rutte and Kellogg are in the European theatre does not exist in this administration. Moreover, attempts by Trump in his previous administration to negotiate a change in the relationship with the DPRK and to convince them to abandon their nuclear programme fell flat, which dampens any enthusiasm to re-visit that issue. It is not immediately evident if there is a comparable commitment in the administration that seeks to secure the peace in Asia that is equal to the efforts to make peace in Europe. The lack of a force-on-force conflict in Asia comparable to what is happening in Ukraine also assures that the European theatre will remain a higher priority until there is some resolution to Russia’s invasion of February 2022.

Trump has not been inclined to put significant effort into policy formulation for some of the regions in Asia. The assessments from some is that he has little to no interest in Southeast Asia in particular. The conclusion of some of the major allies in the region is that if there was no threat from the PRC and without its growing presence and pressure on US allies like the Philippines – not to mention the ROC – there would be even less attention paid to issues like the trilateral alliance in Washington.

This trilateral arrangement is of inestimable significance to the situation in Asia, to the maintenance of the long-running security cooperation that the US has enjoyed with both the ROK and Japan, and – although there is not always adequate acknowledgement or awareness of it in Washington – to the long-term security interests of the US. If the ROK and Japan are to continue the bridges built between them and the US in these past years it seems they will have to shoulder more of the burden. This would require then to not only continue to strengthen the alliance, but also the arduous task of explaining to US policy makers why this three-nation alliance is as more important today than it ever has been.

 

Recommendations

1) The ROK-Japan-US trilateral alliance will need to do more to publicise and conduct public education and diplomacy to promote its maintenance and to continue it being as priority. Equally important will be the need to emphasise the benefits of the alliance to all parties, particularly as its benefits for the US. Creating awareness of how the alliance creates synergisms with the US forces in the region that permit them punch above their weight is another narrative to be articulated. 

2) As pointed out above, the ROK has one of the most well-developed and impressive defence industrial bases of any of Washington’s Asian allies. Unlike Japan, which has a constitution that forbids it to export weaponry, the ROK not only has no legal restrictions to export weaponry, but Seoul’s defence companies have the declared intention to aggressively expand their export customer base. This perhaps presents a solution to a difficulty that Washington faces in Asia. 

The US allies in the region which have limited budgets and too much territory to defend against the PLA desperately need an accurate, effective anti-ship missile. Most of them cannot afford a US weapon like the AGM-158C LRASM, and even if they could the US would probably not sell it to them out of concerns for compromising technology. An ROK-made weapon and other types of systems as well could solve this problem for these countries and elevate the ROK’s perceived value to the US in the process. 

3) Another possibility is using the model recently adopted by the US and Israel to jointly produce the Bullseye precision long-range cruise missile in the US. The missile is designed by Rafael in Israel, but it will be cooperatively produced in the US by General Atomics. The US has its own problems with munitions shortages with supplying both Ukraine and Israel in current conflicts plus the needs of the US Navy fighting against Houthi rebels in the Red Sea. The name of the game in the present day is how to build out more production capacity for major high-value weapon systems. The question is how the ROK could similarly work with US industry to relieve some of the stresses on the US military.

4) Security conferences like the Warsaw Security Forum and Shangri-La Dialogue in Singapore are widely covered in the media and are attended by many senior US defence and foreign policy officials. More panels and roundtables at these events that focus on the importance of the ROK-Japan-US trilateral alliance is another way of not only raising awareness that goes beyond public education campaigns. It goes a step further than public education and diplomacy campaigns in that the issues are being discussed face-to-face in front of these senior military leaders and policy makers. That kind of proximity can make a considerable impact. 

5) Keeping the ROK-Japan alliance and the importance to the US in the front of the decision-makers in Washington is also a job for professional lobbyists. The ROK are no strangers to lobbyists in the defence arena. The history of this activity goes back at least as far as the mid-1980s when the ROK. In this time lobbying was focused on convincing the US Government to issue the necessary export licences and sign off on technology transfer requests so that the ROK could have their own production line in-country for the F-16. This turned out to be a highly-productive partnership that continues to this day. 

6) The other major foreign policy and defence dilemma for the US in Asia is the ROC. The importance of the ROC to US industry and to the US armed forces’ strategy to defend the First Island Chain is paramount. Part of any effort to convince Washington of the vital interests that the ROK-Japan-US alliance represent is to elaborate in detail the degree to which Washington would depend on these two Asian allies to defend the island from an invasion by the PLA. The fact that the ROC cannot be saved from a PLA invasion without them is an issue that should be emphasised.

At present there is substantial realisation within some agencies and institutions in Washington that what happens in the Asian theatre of military operations is of vital importance. Our allies in Asia can make all the difference in the US achieving its objectives in the region. The ROK would do well to focus some effort in assisting these US institutions in convincing their leaders and policy makers of that fact.

 

Author: Reuben F. Johnson 

Director of Asia Research Centre, Korea Fellow, 

Casimir Pulaski Foundation

 

This research was supported by the Korea Foundation

 

Bibliography

[1] Sakata Yasuyo, “The US-Japan-ROK Trilateral After Yoon: Japan’s and Korea’s Security Choices in the Trump 2.0 Era,” nippon.com, 14 May 2025.

[2] The Australian National University Editorial Board, “Signs of convergence on South Korean foreign policy strategy”, East Asia Forum, 9 June 2025.

[3] Reuben F. Johnson, Korean Aerospace Industries eyes new fighter designs, FA-50 sales in Pacific, Breaking Defense, 1 June 2023.

[4] 중앙일보, 북·중·러가 자극한 한·미·일 결속 [출처:중앙일보], The JoongAng, 25 August 2023.

[5] Сергей Шелин, “Центробанк: мемуары о том, что произойдет в 2025 году”, The Moscow Times, 5 September 2024. 

[6] Alexander J. Motyl, “Russia’s Coming Deputinization,” Facts and Arts, 16 May 2021.

[7] “Nothing will change in Russia after Putin leaves – Budanov”, UkrInform News Agency, 2 August 2025.

[8] Reuben F. Johnson, “‘Putin Is Mocking You’: The 4 Words That Sparked Trump’s Dramatic U-Turn On Ukraine,” National Security Journal, 27 July 2025.