Introduction: What Comes After New Theory of War

In 2025, Japan began a new chapter in its postwar political history. Sanae Takaichi was selected as the Liberal Democratic Party’s 29th president in the party’s presidential election and assumed office as Japan’s 104th prime minister. The appointment of the first female prime minister in Japan’s history as a constitutional state is more than a symbol of gender equality: it marks a historical turning point in the principles underlying Japanese politics and foreign policy. The new Takaichi administration should seize this historical moment, confront the new realities of an international society that is increasingly fractured and contentious, and carve out a new direction for Reiwa-era diplomacy marked by dialogue and connection. In setting the course of Japanese foreign policy, the appointment of the “First Female Premier” carries civilizational weight beyond mere political symbolism.

Prime Minister Takaichi vigorously kickstarted a flurry of diplomatic activity only five days after assuming office. Beginning with the Association of Southeast Asian Nations (ASEAN) Summit, she went on to have talks with US President Donald Trump and then attended the Asia Pacific Economic Cooperation (APEC) summit; this packed diplomatic schedule signaled a new phase called “Takaichi Diplomacy.” Her appearance on the world stage facing world leaders as the new face of Japan symbolized a turning point in Japan’s postwar diplomacy.

The 21st-century international order is entering a phase in which one cannot simply speak of “peace” and “stability.” Reignited great-power confrontation, emergence of non-state actors, global challenges such as climate change and infectious diseases, and expansion of information warfare in domains such as AI and cyberspace are simultaneously coming to the fore in our present day. The line between war and peace has become more blurred than ever, and traditional security studies cannot include such a reality within its boundaries. The war in Ukraine has indicated that great power war is not a “relic of the past,” and the conflict in Gaza has demonstrated that violence from non-state actors can rock the very foundations of the international order. The isolationist tendencies of the United States, rise of emerging powers such as China and India, and growing prominence of countries referred to as the Global South have revealed the difficulty of regulating the international order according to a single set of values.

This structural transformation becomes clearer if we focus on BRICS, of which many countries in the Global South are member states. According to a 2024 estimate by JETRO, the BRICS countries are home to 3.5 billion people, or 45% of the world’s population, and their combined GDP exceeds US$28 trillion. Although BRICS is actively growing as a core framework for the Global South, differences in the values and political positions and diversity in religion and culture among its member states have led to various forms of friction. Thus, the formation of an integrated order remains unstable.

In addition, the geopolitical challenges facing Japan have grown more complex, including an arms race in East Asia, tension in the Taiwan Straits and on the Korean Peninsula, and uncertainty in the supply of energy. Further, a declining birthrate and aging population have shaken the foundations of Japan’s security. Considering this reality, with its complex combination of risk and opportunity, revisiting the late Kenichi Ito’s New Theory of War (2007) has become highly meaningful.

The book was a pioneering work written against the backdrop of the confusing state of affairs after the Cold War. It advanced a unique perspective that war is not an inescapable part of our destiny but a phenomenon that arises only when certain social, technological, and political conditions are fulfilled. Thus, war arose from the process of humanity’s evolution from “unconnected herds” to “institutionalized groups”; it changes in its form as conditions do and may even disappear. Ito re-examined war on the scale of human history—tracing the changing meaning of war as a social phenomenon from the Peloponnesian War in Ancient Greece, through the Thirty Years’ War in early-modern Europe, and to the two world wars. Based on this, he proposed the idea of “active pacificism.” This idea does not simply refer to military buildup but to the eradication of the conditions that lead to war in the first place. This idea meant that peace should not be considered as “someone else’s problem” but as a task that Japanese people must “conceptualize and act upon for themselves.”

Considering this perspective in the realm of Japanese foreign policy, postwar Japan has lived with the US–Japan security alliance and Article 9 of its constitution to maintain a framework of being a non-military state. However, through Japan’s more active international role after the Gulf War, its PKO act, and its advocacy for human security, Japan has sought ways to transcend a postwar regime of passivity and engage proactively in shaping the international order. New Theory of War emerged at this juncture of Japanese history and served as a catalyst to awaken Japan’s “power to conceive” its foreign policy vision.

However, today, the environment in Reiwa Japan has become even more severe. The recurring “discontinuity of governance” in Japan, as exemplified by the short life of the prior Ishiba administration, risks damaging Japan’s credibility on the international stage. Therefore, whether Japan can institutionalize its diplomatic vision to persist across changes in administration should be considered. An important challenge facing contemporary Japan is precisely whether it can maintain and strengthen the governing capacity needed to maintain a durable and highly networked diplomatic strategy.

This article draws on Ito’s insights to examine new strategic challenges stemming from an age of “composite crises” in the 21st century. The watershed for whether Japan drifts along as “a state caught in between” or participates in shaping the international order as “a builder of bridges” depends not only on the three pillars of Japanese foreign policy—of strengthening the US–Japan alliance, achieving a free and open Indo-Pacific (FOIP), and working with the Global South—but also on networked engagement with Eurasia (Eurasian diplomacy for the Reiwa era) and the concrete realization of the concept of human security and the Women, Peace, and Security (WPS) agenda.

However, the insights from New Theory of War are, in some respects, approaching their limits in our present day, nearly 20 years after its publication. AI, space, cyberspace, and the growing strategic autonomy of the Global South are elements that it could not have anticipated in its time. Thus, to discuss the international order in the Reiwa era, we must build on Ito’s theoretical framework while supplementing it with new conditions, thus pointing the way toward what may be called A Sequel to the New Theory of War.

Considering this era situated between war and peace, we bear the responsibility of not only examining Ito’s insights but also of updating and transcending them.

１．The Framework of New Theory of War and its Contemporary Significance

(1) The Emergence and Background of New Theory of War

New Theory of War emerged at a time when the international order appeared to be shifting into a “unipolar era” after the end of the Cold War. However, a continued series of tragedies such as the conflict in Yugoslavia and genocide in Rwanda rapidly dispelled any illusion of a post-Cold War peace, bucking expectations of the United States’ unipolar dominance following the fall of the Soviet Union.

We often hear claims that “war has changed the conduct of international politics.” However, Ito states that war is a necessary consequence of the social phenomenon that is international politics; specifically, unlike domestic politics, where conflict is resolved through institutionalized processes, international politics is such that conflict can only be resolved through military force in the form of war. Thus, he argued that the problem of war cannot be overcome unless the institution of international relations itself is transformed.
Regarding the relationship between war and “international politics” or “international relations,” I would like to emphasize that war, as a social phenomenon, has always been linked to structural shifts in the international order.

For example, the Peloponnesian War shook the city-state system in Ancient Greece, Wars of Religion led to the modern system of sovereign states, and two world wars led to the dismantling of the imperialist order and creation of the United Nations system. These function as evidence that war is a mirror that reflects transformations in order. This idea resonates strongly with Western views of war. Thucydides portrayed war as a transformation in the balance of power, and Clausewitz defined it as “the continuation of politics by other means.”

Moreover, the notion of war as a phenomenon of order resonates with East Asian thought. According to Sun Tzu, “To fight and conquer in all one’s battles is not supreme excellence; supreme excellence consists in breaking the enemy’s resistance without fighting.” Here, the essence of war is framed not as attrition through military might but as a “technique of governance” that incorporates information, psychology, and diplomacy. In addition, Takeda Shingen’s motto “as swift as the wind, as quiet as the forest, as fierce as fire, and as steadfast as the mountain” and the Yangming school’s saying that “soldiers are instruments of benevolence” sought, as did Sun Tzu’s The Art of War, to situate war in the context of order and ethics.

In this respect, as we attempt to comprehensively understand the increasing complexity of modern conflicts, we must remind ourselves that war occurs together with the conduct of international politics. We can help the Japanese public cultivate a flexible and multi-faceted conception of war, by weaving together East-Asian and Western thought—by supplementing Clausewitz’s central thesis with Sun Tzu’s emphasis on information, psychology, and governance. Consequently, this can lead to the intellectual foundations that Japanese foreign policy can depend on.

(2) Issues Confronting Japanese Foreign Policy

I have long been searching for answers on how Japanese foreign policy ought to be from the perspective of Track II diplomacy. At the root of this search lies a searing reflection on postwar Japan’s strategic passivity, as exemplified in criticisms that Japan had “only given its treasure and not blood” in the Gulf War, its failure to acquire a permanent seat on the UN Security Council, and its equivocal involvement in the Iraq War. These events are symbolic of a Japan that has settled into a “postwar regime” and lacking the power to conceive how it can proactively shape the international order.

Traditional international relations theory has centered on a Western paradigm of sovereign states, hegemony, and great powers. However, the rise of the Global South and the increasing prominence of non-Western conceptions of order have exposed the limits of this logic of “domination and balancing.” Increasingly, the reality of international politics is found not in the projection of power but in precisely the dynamic interaction between relationality, coexistence, and coordination. Thus, the starting point for the next phase of Japanese foreign policy lies in visualizing those relations emerging from the interstitial spaces between competing states and values—that is, in visualizing that dynamism between coordination, mutual resonance, and emergence.

Japan has explored its own room for diplomatic maneuver while being a quintessential “in-between state”—positioned in between and occasionally buffeted by multiple great powers and pivotal states. In the post-Cold War order, Ukraine, Georgia, Armenia, the Central Asian states, and countries in Africa and the Middle East have also been quintessential “in-between states” that have sought to expand their strategic autonomy while operating in the cracks between rival great powers. As competition between China and the United States heats up and as Japan continues to live in an unstable neighborhood alongside Russia and the Korean Peninsula, Japan will need to consider whether it will be passively tossed about or leverage its “in-betweenness” and transform it into strategic autonomy.

The significance of New Theory of War lies in how it speaks directly to this question. During its publication in 2007, the world was steeped in the lingering echoes of a unipolar order. However, the international environment has since undergone an upheaval. The war in Ukraine represents not only the return of great power war but also the development of “hybrid warfare,” marked by cyberwarfare and disinformation campaigns. Moreover, the conflict between Israel and Hamas has laid bare the reality that violence from non-state actors has rocked the foundations of the international order. The tug of war over drones, AI weapons, space, and cyberspace is increasingly redefining the meaning of war.

Furthermore, US domestic instability, the rise of China, and growing strategic autonomy of the Global South are intersecting to produce a multipolar order that would have been unfathomable to anyone in 2007.
In such complex times, Japanese foreign policy is confronted not simply with considering which side it is on but rather with the challenge of how it can shape its “in-between-ness” to become an autonomous subject that connects parts of the international system together. This entails becoming a “mediating actor” that creates new channels of engagement in the fissures opened up by rival blocs and possibly becoming a bearer of a “connective international order” that softens ruptures between states.

(3) Contemporary Challenges

As the international community transitions toward a multipolar order, Japan must not only center itself on its alliance with the United States but also calibrate its relations with China and Russia and strategically formulate linkages with Central Asia, the Middle East, and Europe. In this process, multiple layers of issues surrounding security, energy, the economy, and norms-based diplomacy intersect, and a simplistic policy of merely hewing to the United States and deterring China would fall short in addressing them. It is precisely because Japan is situated between the great powers that it has room to leverage the dual nature of interdependence and friction to become an agent with a hand in shaping the international order.

However, today, Japan is once again demonstrating the fragility of its political foundations. The foreign press characterized the abrupt end of the Ishiba administration’s short-lived tenure as evidence of “chronic political instability” and a call for “doubt surrounding (Japan’s) strategic continuity.” Although long-lived administrations, such as those of Nakasone, Koizumi, and Abe, provided postwar Japan with rare episodes of stability, a series of short-lived ones have impeded continuity in national strategy. Thus, how Japan can institutionalize domestic political stability and strategic planning capacity is the biggest blind spot in Japanese foreign policy.

Therefore, for Japan to evolve into being the “autonomous bridge between parts of the international system,” it must overcome its pathology of short-lived administrations and institutionalize its capacity for strategy formulation. In this respect, what matters going forward is how the new Takaichi administration can expand Japan’s menu of foreign policy options.

２．Expanding and Fostering Connectivity in Japanese Foreign Policy

(1) The Apparent Strengths and Underlying Weaknesses of Japanese Foreign Policy

Postwar Japan has accumulated a distinctive stock of diplomatic assets even while operating under constraints on its military. The first is Japan’s engagement in “coordinative diplomacy.” During the Cold War, Japan sought points of contact with non-aligned countries through economic cooperation with Southeast Asia, and after the Cold War it was an active participant in multilateral frameworks. Japan has transformed its limitations as a quasi-non-military state into a strength: its foreign policy is characterized by fostering consensus not through hard-power balancing but by its role as a mediator between competing interests.

The second is normative credence forged through a foreign policy of human security. In an era marked by an uptick of civil wars and weak states, Japan has given international society a new normative resource in the form of its diplomatic philosophy centered on the dignity of the individual. Its leadership in the United Nations and in providing development aid has been highly valued and has made Japan a key player in norms-based diplomacy.
The third lies in the accumulated fruits of its ODA diplomacy. Through engagement in infrastructure projects, support in education and health, and participation in environmental initiatives, Japanese aid has transcended mere financial transfers to become a pillar of confidence building and regional stability. Although Japan’s comparative advantage has diminished in the face of China’s Belt and Road Initiative, the traditional hallmarks of Japanese aid as being of “high quality” and rooted in “cooperation on the ground” remain a major diplomatic asset.

However, we must not ignore the inescapable structural constraints under which Japanese foreign policy operates.

The first is population decline and economic stagnation. A shrinking economic base eats away at the foundation of Japan’s international influence and stock of diplomatic resources.

The second is military constraints. The Self-Defense Forces have undergone modernization but their deployment in collective self-defense remains limited; this limits Japan’s ability to deal with the great powers.

The third is limits placed by public opinion. Public caution regarding overseas deployments and the use of military force has pushed Japanese foreign policy toward a “better safe than sorry” posture.

A further institution constraint that deserves attention is the pattern of short-lived administrations. Many Japanese cabinets have been too short-lived to leave behind any tangible diplomatic achievements, and this structural problem of a lack of strategic continuity that they have exposed cannot be ignored.

(2) The Means and Meaning of Turning Weaknesses into Strengths

Constraints are not always weaknesses. Japan’s key diplomatic assets have been forged within these constraints. Precisely because of Japan’s limited military capacity did it develop its coordinative diplomacy approach and a values-based foreign policy centered on human security. Furthermore, Japan has made notable contributions to the WPS agenda in recent years. Since its ratification of the WPS resolution, Japan has formulated three successive action plans and implemented proactive measures to discharge its commitments under the resolution. These efforts have been wide-ranging, involving responses to climate change, natural disasters, and crises from armed conflict as well as initiatives in human resource development aimed at popularizing the WPS agenda. Even if Japan’s relative economic position declines in the future, its flexibility in delivering high-quality aid and engaging in trust-building diplomacy will remain unshaken.

The problem of short-lived administrations, paradoxically, highlights the importance of diplomatic assets that do not depend on any single institution. Foreign policy grounded in networks comprising academia, civil society, international organizations, and the civil service can persist beyond the life of any one administration. One task for Japanese foreign policy is to build an “architecture for diplomatic continuity” based on a recognition of Japan’s limitations.

The meaning of Japanese foreign policy lies not in a simple dichotomy of strengths versus constraints but in the use of both as part of a wider strategy. Japan’s coordinative diplomacy approach is valued precisely because it rests on the premise of constraints on its use of military force, and its accumulation of diplomatic assets that lie outside the formal political system can serve as both its strength and a buffer against the weakness of short-lived political administrations. Therefore, Japan’s distinctiveness resides in its ability to “turn constraints into resources.” As an extension of its vision of an FOIP, Japan must also explore a new strategy of creating a space for collaborative dialogue with the Global South and jointly advance the competing objectives of “institutional inclusion” and “a shared set of values.”

A strategy of transforming one’s weaknesses on their head to establish one’s agency while caught in between the great powers (and other state actors) is indeed a strategy that is suited to present-day Japan. As I argued in my essay “Japan’s Choice of ‘Eurasian Diplomacy’” (Chuokoron-Shinsha, 2022), Japan’s mission is not to passively follow along with a changing international order but to harness its strengths and constraints as strategic resources to exercise its agency (i.e., to play a proactive role) in a fluid international order.

3. The Core of a Reiwa-Era New Theory of War

(1) Japan’s Self-Conception as a State with Both Strengths and Limitations

In considering Japan’s position in a Reiwa-era international order, we must first begin with the characteristics of its strategic and geopolitical situation. During the Cold War, Japan prospered under the US–Japan security arrangement as a “major economic power” and “minor military power.” However, at the dawn of the 21st century, Japan faces a world where a strategy of “going all in on a single alliance” is insufficient to secure its interests amid a decline in the United States’ relative position, the rise of China, resurgence of Russia, and growing autonomy of the Global South.

As evident in the United States’ turn inward and a “Trump 2.0” administration, the iron-clad nature of the US–Japan alliance cannot be taken for granted. Faced with such uncertainty, Japan must now transform its awareness of itself as a state with both strengths and constraints into a strategic asset.

At first glance, the constraints faced by postwar Japan—legal norms, limitations on its use of force, and economic dependence—highlight its vulnerability. However, their “institutionalized restraint” has led to moral credibility. To say that Japan is a state that configures that “space in between” is simply to say that it is determined to play a part in the international order without the use of hard power. This perspective is one wellspring from which a distinctly Reiwa-era Japanese foreign policy can take shape.

(2) A Dual Strategy Based on Multilateral Diplomacy and the US–Japan Alliance

What strategy should Japan adopt? One answer is to add a perspective of what I call “connective diplomacy” to the three aforementioned pillars of foreign policy, thus allowing Japan to transcend the dichotomy of “alliance or autonomy.”

The US–Japan alliance remains foundational to Japan’s foreign and security policy. Cooperation with the United States is indispensable for deterring attempts to revise the status quo by China as it builds up its military and by North Korea as it test-fires nuclear and ballistic missiles. However, there are issues that the alliance alone cannot resolve. Non-traditional security challenges, such as climate change, infectious diseases, migration and refugees, and resource and food security, cannot be addressed by the logic of military deterrence.

Thus, Japan must center its foreign policy around the alliance while pivoting to form multilayered networks with actors, such as BRICS, ASEAN, the EU, and countries in Africa and Central and South America—thus transforming itself into “a diplomatic player that bridges gaps between rival blocs.” The “connectivity” that I envision is first and foremost an ethic and only then a strategy; it is a determination to shape the world together with others. This is the concrete expression of the ambition of “a foreign policy that transforms the conditions giving rise to war” set out in A Sequel to the New Theory of War.

(3) Combining Eurasia Diplomacy, the WPS Agenda, and SDGs

In such a context, new strategic resources for Japanese foreign policy are emerging, that is, “Eurasia diplomacy” and international norms such as the WPS agenda and SDGs.

Eurasia had long fallen outside the radar of Japanese diplomacy; however, today, the region is re-emerging as a strategic focal point encompassing issues pertaining to resources, infrastructure, security, and cultural pluralism. Eurasia is a geopolitical space including Russia, China, Central Asia, and Central and Eastern Europe that is indeed symbolic of the “in-between spaces” in the international system.

The WPS agenda and SDGs are normative frameworks that constitute a non-military domain in which Japan can assume a leading role. The WPS agenda incorporates the perspective of gender into peacebuilding, disaster response, and conflict prevention and dovetails naturally with the idea of human security. Similarly, the SDGs, which range across the domains of development, social inclusion, and the environment, can become a stage on which Japan institutionalizes international trust.

What matters is not to treat these as separate initiatives but to integrate them under a shared “philosophy of connectivity.” Japan can establish itself as “a security actor that centers the human being,” by ensuring sustainability in its resource diplomacy, promoting the WPS agenda in multilateral cooperation, and positioning the SDGs in the mainstream of its diplomacy. In this respect, Eurasia is not merely a geographical region; it is an ideal of institutionalized coexistence.

(4) The Core Proposition of a Reiwa-Era New Theory of War

The core of a Reiwa-era New Theory of War lies in the following: Japan should transform its position as an “in-between state” into a strategic asset to become a “proactive shaper of the international order.” It should do so through Eurasian diplomacy, the WPS agenda, and the SDGs while centering its foreign policy on the twin pillars of connective diplomacy and the US–Japan alliance.

Today’s wars are multilayered, involving not only inter-state conflict and violence by non-state actors but also non-military crises such as climate change and pandemics. Thus, in this context, Japan should not be a “passive follower,” but contribute to the shaping of the international system as an “active architect.”

Constraints such as an aging population and limits on its military buildup can, conversely, become a resource by serving as grounds for Japan to take the lead in non-military domains. To shape the international order by means of ideas, institutions, and cooperation, rather than military force, is the central proposition of the Reiwa-era New Theory of War.

As Japanese diplomacy eventually came to be praised for its “ability to get things done” in Cold War–era negotiations, Japan is once again being called on to demonstrate its capacity for strategic imagination from within the interstices of history. Precisely because of the instability in the international order today, Japan bears the responsibility of sketching out a new vision of coexistence through “the power to connect” and “the power to mediate.” The historical task of Reiwa-era Japanese diplomacy is to unearth the seeds of strategic imagination that lie hidden in the shadows of short-lived administrations and cultivate them into a strategy for the next generation.

Conclusion—Toward a Sequel: A Vision for the Future of Japanese Foreign Policy
From New Theory of War to A Sequel to The New Theory of War

In the present Reiwa era, the fundamental question we must ask is: “How should Japanese foreign policy confront this transforming relationship between war and order?” This article has attempted to take up the mantle of Kenichi Ito’s thought and explore how Japan can leverage its uniqueness as an international actor in the face of the multilayered complex of risks in the 21st century. In New Theory of War, Ito asked the basic question: “Can Japan remain a mere bystander to the international order?” We in the Reiwa era are being asked the very same question but in circumstances far more complex than those in Ito’s day.

In an age of “multilayered risks” with returning great-power war, expanding violence by non-state actors, and increasing global challenges, Japan’s role is not that of a direct party to war, but that of a designer of a new order that transcends the binary of war and peace.

The guiding principles that Japan should advance in such an endeavor are “coordinative capacity” and “human-centeredness.” Rather than flaunting its military power, Japan should present inclusive frameworks that connect different values and institutions. Rather than only preserving state security, Japan should construct security arrangements that protect our everyday lives and the dignity of the human being. These are strengths that Japan has honed over its history, and they lie at the heart of the Reiwa-era New Theory of War.

Japan, by actively embracing its status as an “in-between state,” can participate in shaping the order by being a bridge linking Europe, Eurasia, Africa, the United States, and the Global South. Such a posture transcends the dichotomies of war versus peace and alliance versus autonomy and constitutes a vision that Japan ought to pursue.

In the afterword to New Theory of War, Ito wrote the following about the word “new” in the book’s title.

“Amidst the many theories of war out there, I have deliberately chosen to send this work out into the world with the word “new” in its title because I harbor the hope that this will be the last theory of war.”

Amid the disarray of the Reiwa-era international order, we continue to find ourselves compelled to speak of “A Sequel to the New Theory of War.” However, this is not contrary to Ito’s wish. Rather, it is an attempt to inherit Ito’s thought to reconceptualize a foreign policy that does not merely deter war but transform the conditions that lead to war.

Once again Japan stands in the interstices of history. However, this interstitial space is also that blank canvas on which the future can be designed. From here begins a new chapter of Reiwa-era Japanese foreign policy. (End)