In contemporary debates on the Indo-Pacific, decision-makers sometimes invoke the lessons of the 1930s—mostly as a warning against “appeasement.” However, such a frame is too narrow. The failure of Europe’s interwar period originated from the debacle of the entire deterrence structure, not from a single diplomatic miscalculation—political commitment, military planning, and industrial capacity were not aligned within a consistent framework. The end result was the systemic crumbling of the European security order from 1919 to 1939.
Today’s East Asia is faced with a remarkably similar structural risk. While the probability of a dual contingency—China taking military action against Taiwan and North Korea escalating tensions on the Korean Peninsula, whether in a concurrent or sequential manner—cannot be ruled out, the United States, Japan, and South Korea are confronted with a fundamental question: are they structuring a sustainable deterrence system, or replicating a house of cards that neutralized interwar Europe?
A closer examination of four crucial cases reveals how selective commitment, fragmented diplomacy, exclusionary decision-making, and delayed response cumulatively eroded deterrence. The lesson is far from abstract—it is directly connected to contemporary East Asia’s vulnerability.
The first lesson emerges from the Locarno Pact. In 1925, the Western European powers intended to stabilize Europe by guaranteeing Germany’s western border, yet leaving the eastern front—which included Poland and Czechoslovakia—practically outside the security architecture. Temporarily, some degree of stability was ensured in Western Europe. However, Eastern Europe was left exposed, ultimately inviting revisionist pressure.
A similar danger remains today. Although the US commitment to extended deterrence for Japan and South Korea is institutionalized, clarity surrounding simultaneous contingencies—particularly regarding Taiwan—remains uneven. If US commitment is perceived as being tiered either geographically or operationally, the credibility of deterrence would easily crumble in a crisis. The lesson of Locarno is not that guarantees are meaningless, but that selective assurances could create strategic fissures that could be exploited by adversaries.
The second lesson can be extracted from the 1935 Anglo-German Naval Agreement. By signaling a bilateral naval arms control agreement with Germany, Britain effectively undermined collective efforts to deter German rearmament. Although the agreement was intended for stabilization, it instead signaled that Britain could weaken coordination with France and that great powers could bypass collective mechanisms if necessary.
A similar risk exists in East Asia. A crisis-management agreement exclusively between the US and China, or an agreement confined to US–Japan cooperation, may marginalize South Korea and attenuate trilateral cohesion. In a multi-theater environment, deterrence cannot be sustained by ad hoc bilateral agreements. The experience of the interwar period demonstrates that if bilateral agreements—even if they are well-intentioned—are not incorporated into a broader strategic framework, the credibility of the security structure could be severely eroded.
The third lesson is the most widely known, yet often misunderstood case: the 1938 Munich Agreement. The problem at Munich was exclusion, not mere concession. Czechoslovakia—whose territory and sovereignty were at stake—was barred from participating in the agreement that determined its fate. This decoupling of decision-making led to a collapse of trust and, ultimately, deterrence.
This dynamic could be repeated. While a Taiwan contingency would likely to impact South Korean security in a direct fashion, there exists a possibility that Seoul would be treated as a secondary actor. Meanwhile, in a Korean contingency, cooperation with Japan might be insufficiently embedded. If key stakeholders are excluded from the crisis-response framework, this would cause fragmentation instead of ensuring efficiency. Munich’s lesson is institutional—if those most exposed to risk are excluded from decision-making processes, a sustainable security framework cannot be built.
The fourth lesson arises from the remilitarization of the Rhineland. At the time when Germany remilitarized the Rhineland in 1936, it remained relatively fragile. If Britain and France had collectively responded firmly, history might have taken an alternative path, at a relatively affordable price. Nevertheless, by choosing not to take action, they signaled that treaty violations would be condoned, eventually emboldening further aggression.
In today’s context, gray-area provocations—North Korea’s drone incursions, cyberattacks, and China’s maritime militia activities, etc.—represent similar early-phase challenges. These activities are easily overlooked since they often remain below the threshold of all-out war. Nonetheless, the interwar period clearly shows that if non-responsiveness to gradual violations accumulates, deterrence will erode while rapidly increasing the price of future responses.
Taken together, the four cases illustrate one common pattern. Deterrence does not crumble in a single moment, but slowly decays through cumulative disparities among commitments, coordination, and trust. To prevent similar consequences from occurring in East Asia, country-specific policy adjustments—not rhetorical convergence—are necessary.
For the United States, the challenge is to avoid the trap of selective commitment and delayed mobilization that characterized British strategy in the interwar period. To that end, Washington needs to explicitly articulate its approach to multi-contingencies that include Taiwan and the Korean Peninsula. This does not mean a rigid, formal commitment. Nevertheless, it does require clearer signals both toward its allies and potential adversaries alike that US strategy is not geographically compartmentalized. In parallel, the United States should strengthen pre-delegated logistics and sustainment mechanisms, ensuring the large-scale delivery of munitions, maintenance, and operational support from the early stages of conflict. The industrial shortcomings—where rearmament lagged behind strategic necessities—of the 1930s provide a clear warning.
In the case of Japan, the fundamental task is to heighten operational integration within the trilateral framework that goes beyond the traditional role of strict rear-area support. To be sure, Japan has made notable progress in this field by adopting OPLAN 5055 and revising the US-Japan Defense Guideline in 2015. During the interwar period, Britain limited the effectiveness of its deterrence due to reluctance to commit to continental defense. Likewise, although Japan is strategically indispensable, it could face similar risks if it remains operationally constrained. Moreover, Japan should play a proactive role in institutionalizing trilateral defense industrial cooperation with the US and South Korea—in particular, production, maintenance, and supply chains should be operated in an integrated manner. Fragmented armament was a quintessential shortcoming of interwar Europe. In that sense, Japan’s recent decision to lift its ban on exporting lethal weapons to 17 countries should be coordinated with South Korean counterparts so that both countries can avoid excessive competition and instead find ways to create synergy in the long run.
For South Korea, the fundamental challenge is to avoid strategic marginalization. The analogy with 1930s Czechoslovakia is an issue of exclusion rather than vulnerability. Seoul should proactively participate in regional crisis-response planning—especially related to Taiwan. Such an approach should reflect South Korea’s geopolitical constraints and begin by discussing indirect ways to contribute—such as facilitating the relocation of USFK to Taiwan Strait or dispatching destroyers to safeguard sea lines of communication (SLOC)—instead of directly sending combatants into a warzone. At the same time, it should reduce overreliance on external guarantees by developing indigenous ISR and long-range strike capabilities. Finally, Seoul should more explicitly link Peninsula defense to the regional security structure, underscoring that South Korea is a central—not peripheral—actor in East Asian deterrence. If these efforts do not come into fruition, perhaps Seoul should fully prepare to defend against a North Korean invasion without expecting outside assistance.
The tragedy of the interwar period was not simply that leaders took wrongful decisions, but that political will, military capacity, and industrial foundations failed to construct a system capable of aligning these elements. By the time Germany invaded Poland in 1939, the deterrence framework was already in shambles.
East Asia today stands at a similar crossroads. The matter at hand is not whether the United States, Japan, and South Korea recognize the looming threat, but whether they can build a consistent and integrated deterrence framework before the risk factors coalesce. If they fail, the harsh consequences of the interwar period will once again demonstrate themselves in East Asia.
