Periods of structural instability tend to expose the difference between formal alliances and functional strategic partnerships. In the early 1960s, at the height of the Cold War, US President John F. Kennedy and British Prime Minister Harold Macmillan maintained a transatlantic relationship that contributed to managing one of the most dangerous crises in the nuclear era. Their partnership was not based on equality of power, ideological sentiment, or outright alignment. Instead, it was established upon continuous consultations, mutual political restraint, and a shared perception that alliance cohesion matters most when national interests diverge.
Such historical experience holds growing relevance to today’s East Asia. Japan and South Korea are situated within a security environment that is shaped by nuclear-armed North Korea, an assertive China seeking to revise regional norms, and Russia, which is sowing instability beyond Europe. Although both countries are firmly anchored as US allies, the relationship between Japan and South Korea often lags behind strategic demand. The Kennedy-Macmillan experience offers a useful analytical tool to think about how Tokyo and Seoul could move from fitful cooperation to a durable strategic relationship.
Crisis Leadership and the Discipline of Alliance Management
The Kennedy-Macmillan relationship was continuously tested from its early phase. The 1961 Berlin Crisis and the 1962 Cuban Missile Crisis well demonstrated how regional confrontation could rapidly turn into a systemic threat. What distinguished the US-UK relationship at the time was not the absence of disagreement, but the discipline with which disagreements were managed. Macmillan did not simply acquiesce to Washington’s decisions: he conveyed Europe’s threat perception and political restraints and proactively influenced US decisions. Kennedy too perceived the UK’s opinion as a strategic asset and did not treat it as symbolic support. Communication was constant, honest, and institutionalized, extending beyond leaders to advisors, diplomats, and military planners.
Importantly, such partnership balanced deterrence with restraint. The two leaders fully understood that trust does not necessarily require a maximalist posture and that escalation control itself is a form of strength. Rather than identical policies, strategic alignment meant ensuring that one ally’s actions would not undermine the other’s security calculation. Such logic enabled allies to have leeway in diplomacy while projecting resolve against adversaries.
Despite different regional and historical contexts, today’s Japan and South Korea are faced with similar challenges. North Korea’s nuclear and missile programs compress decision-making timelines while increasing the cost of misjudgments. China’s growing military presence and its economic influence are reshuffling the strategic environment of East Asia as well as the Indo-Pacific region. Russia’s activities—strengthening alignment with authoritarian states and its willingness to employ coercion—add another layer of unpredictability. Such pressure endows greater importance on consultation between Tokyo and Seoul, where security interests are more overlapping irrespective of occasional political friction.
Nonetheless, unlike the US-UK relations in the early phase of the Cold War, Japan and South Korea lack a deeply institutionalized habit of strategic consultation. Engagement between the two often remains reactive, triggered by immediate crises or trilateral frameworks spearheaded by Washington. Even when threat perception converged, historical disputes and domestic political sensitivity continuously constrained the level of cooperation. Such a gap between shared interest and practical coordination is becoming harder to sustain.
Applying Kennedy-Macmillan Lessons to Japan–South Korea Relations
The first lesson extracted from the Kennedy-Macmillan experience is the importance of continuous strategic engagement. Effective partnership is established through routine, structured conversation—that shapes how each side interprets the strategic environment—not by occasional summits. In the case of Japan and South Korea, it means moving beyond symbolic gestures of reconciliation toward regularized security consultations at the national security advisor and senior official level. With the passage of time, such a mechanism could produce joint threat assessment and synchronized planning assumptions, ultimately reducing the probability of misaligned responses in crisis situations.
The second lesson is about deterrence. Kennedy and Macmillan understood that deterrence could work only when consistent signals are conveyed to the allies. In today’s East Asian context, especially related to thresholds in North Korea’s use of nuclear weapons, the existing ambiguity between Tokyo and Seoul offers room for adversaries to test resolve. Closer alignment on the deterrence principle does not require identical military doctrine, yet it does necessitate closer redlines, proportional response, and crisis communication. Officially stated and jointly endorsed principles could strengthen deterrence while reassuring the domestic constituencies that escalation is carefully managed.
Domestic politics is often considered an obstacle to cooperation; it could instead turn into an instrument for sustaining it. Macmillan played a crucial role in translating the American strategic necessity into a language that the European public could accept, while Kennedy remained sensitive to the political constraints of US allies. Japanese and South Korean leaders are also faced with domestic skepticism that includes concerns about entrapment, anxiety over rearmament, and weariness toward historical revisionism. A coordinated message—that frames bilateral cooperation as a stabilizing force, rather than an ideological project—could contribute to forging broader political support. Joint statements, shared narratives on regional stability, and coordinated diplomacy vis-à -vis Southeast Asia and other middle powers would reinforce the legitimacy of closer alignment between Tokyo and Seoul.
Practical cooperation also matters. The Kennedy-Macmillan partnership expanded from nuclear strategy toward intelligence sharing, conventional force coordination, and technology cooperation. In the case of Tokyo and Seoul, relatively emerging domains—missile defense integration, cyber security, situational awareness in space, and supply chain resilience—provide opportunity for tangible progress. Such domains are directly connected with shared security concerns, yet politically less charged than, say, historical disputes. In such areas, functional cooperation could accumulate trust that could be expanded toward sensitive fields over time.
The role of the US remains central, yet it should be considered a facilitator rather than a substitute for bilateral initiative. During the Cold War period, US-UK relations functioned as a partnership, providing each side with unique strength, rather than a hierarchical arrangement. Similarly, Tokyo and Seoul should deepen coordination through trilateral frameworks with Washington while taking greater ownership when it comes to bilateral relations. Although trilateral contingency plans, joint military exercises, and integrated early-warning mechanisms could reinforce deterrence, they could ideally operate when Tokyo and Seoul are already aligned at the strategic level.
For Japanese leadership, this means preemptively proposing institutionalized strategic dialogue mechanisms to the South Korean counterparts and investing political capital in consistent engagement. As for the South Korean leaders, it is required to clarify that cooperation with the Japanese counterparts and accepting deepened trilateral or bilateral planning enhance—instead of restraining—strategic autonomy. For both governments, articulating deterrence, economic resilience, and a joint vision on regional order that respects international norms would provide strong signals both to allies and adversaries.
The Kennedy-Macmillan partnership showcases that effective strategic alignment does not necessitate complete harmony. It instead requires discipline, empathy for allied constraints, and the willingness to institutionalize cooperation before crises occur. As East Asia enters an age of heightened uncertainty, Japan and South Korea are at the crossroads. They could continue to rely heavily on ad hoc coordination led by Washington or start to structure a more resilient bilateral partnership that factors in today’s threat environment. History suggests that countries that invest early in strategic cohesion have a greater chance to muddle through when the most perilous moments arrive.
