Table of Contents


Takahashi Sugio
Takahashi Sugio is a research fellow at Japan’s National Institute for Defense Studies and chief of its Policy Simulation Division. He has published extensively in the areas of nuclear strategy, the Japan-U.S. alliance, and East Asian regional security.

Strategic stability is a key concept in nuclear deterrence. But since both words, “strategic” and “stability,” include some ambiguity, this concept has been sometimes misunderstood as a situation of general stability among great powers. But it has specific meanings for experts on nuclear deterrence: crisis stability and arms race stability. Crisis stability represents a situation in which both parties have no advantage from first strike, and neither side has an incentive to start a war. Arms race stability is a situation in which each party’s force structure does not incentivize the other side to expand its military forces, thereby lessening the motivation to start an arms race. These notions about strategic stability were developed during the Cold War, when the United States and the Soviet Union deployed numerous nuclear warheads. At that time, avoiding nuclear war, which could quickly extinguish many human beings, was the primary objective.

In the contemporary world, how to deal with rising China is perceived as a serious strategic agenda item and the notion of strategic stability is applied to Sino-U.S. relations.1 Current Sino-U.S. relations, however, are different from U.S.-Soviet relations during the Cold War, and the concept of strategic stability needs to be redefined. In that process, not just U.S. expert thoughts, but also views from Japan need to be considered because Japan is a key U.S. ally in East Asia and an important piece in East Asia strategic dynamics. The purpose of this piece is to provide an overview of how Japan’s strategists see strategic stability and how they think about redefining it for the contemporary world.

Understandings of Strategic Stability in the Japanese Strategic Community

The intellectual history of the Japanese study of cutting-edge nuclear deterrence theory is not short. While nuclear deterrence has been a very politically sensitive issue in Japan after the nuclear bombings of Hiroshima and Nagasaki, some realist scholars seriously follow it. In 1973, top-ranking experts Momoi Makoto and Kosaka Masataka published a translated book about nuclear deterrence titled Strategy in a Multipolar Era: Historical Development of Nuclear Strategy, issued in two volumes.2 This huge work (553 pages in volume one, and 548 pages in volume two) covers many key articles that played great roles in the development of nuclear deterrence theory, such as Bernard Brodie’s “The Anatomy of Deterrence,” Thomas Schelling’s “The Role of Communication in Arms Control,” Albert Wohlstetter’s “The Delicate Balance of Terror,” Glenn Snyder’s “Deterrence and Defense,” and some chapters from Henry Kissinger’s The Necessity for Choice. While this is a translated work and not an original study about nuclear strategy, its publication suggests that there was a market for such strategic issues in Japan’s intellectual community in the early 1970s.

And during the final phase of the Cold War, the Japan Association of International Relations, which is the biggest academic association on international relations studies in Japan, published a special issue of its journal on “Nuclear Deterrence and Arms Control at a Turning Point.” The issue covered the Intermediate-Range Nuclear Forces (INF) debate, deterrence theories in the Soviet Union, the credibility of a nuclear umbrella, and nuclear arms control.3 Following this, immediately after the end of the Cold War, that generation’s three top nuclear deterrence experts, Ogawa Shinichi, Umemoto Tetsuya, and Ishikawa Shuichiro, published books exclusively focusing on nuclear deterrence.4 As these publications show, even with Japan’s nuclear taboo, studies about nuclear deterrence issues were steadily developed. At the same time, however, these are basically textbooks on nuclear issues and include very few original studies. In this sense, regarding strategic stability, the purpose of these publications was to introduce American thoughts on strategic stability to Japanese audiences.

The only exception was Japanese engagement on the INF issue. During the INF Treaty negotiations, the United States and the Soviet Union discussed an option to relocate their intermediate nuclear forces from Europe, rather than remove them from both Europe and the Far East. At that time, Japan was concerned about this option, and then Japanese prime minister Nakasone Yasuhiro sent a strong message to U.S. president Ronald Reagan that Japan could not accept it. This exception, however, is about a specific policy issue rather than broader strategic concepts such as strategic stability. In this sense, during the Cold War, the Japanese strategic community was in a “receiving mode” for U.S. strategic thoughts on nuclear issues.

One of the reasons, in addition to the nuclear taboo in Japan’s society, was a significant difference in the strategic situation between Europe and Asia. In Europe, where a key theme in nuclear strategic thought was to avoid a nuclear exchange between the North Atlantic Treaty Organization and members of the Warsaw Pact, the question of how to offset conventional inferiority to the Soviet Union was a critical challenge for U.S. strategists. Given the strategic balance in Cold War Europe, nuclear forces were regarded as an indispensable “equalizer” against conventional superiority. Detailed thoughts about the escalation ladder from the conventional level through tactical and theater nuclear weapons to strategic nuclear forces were developed. The concept of strategic stability was to mitigate the incentives for first strike to avoid inadvertent war and to lessen the motivation for an arms race under a strategic showdown.

Meanwhile, in Asia, the strategic situation was completely different. Since Asia was basically a maritime environment, the Soviet Union’s armored divisions had limited strategic implications, even though they were quantitatively (and possibly qualitatively against Japan) superior. In Asia, key elements determining strategic balance were naval and air power. In those capability areas, the United States enjoyed huge advantages over the Soviet Union. Therefore, the United States and Japan did not rely on nuclear weapons as an equalizer to cover conventional inferiority, unlike in Europe. The expectation for nuclear forces in Asia was to deter the Soviet Union’s first use of a nuclear weapon against U.S. superior naval forces.5 Existential deterrence was enough, and it was not necessary to develop a more sophisticated notion of an escalation ladder.

In this context, the reason why Japan had serious concerns about the relocation of the Soviet Union’s SS-20 missiles to the Far East can be easily understood. From the point of view of the Soviet Union, given conventional inferiority, SS-20 deployment in the Far East would have an equalizer effect over American conventional naval superiority. But from Japan’s point of view, it would undermine the foundation of Japan’s strategic calculation.

Japan’s Current View on U.S.-China Strategic Stability

Even after the end of the Cold War, strategic stability between the United States and Russia has continued to be a serious issue in international affairs, and multiple nuclear arms control treaties have been concluded by these two countries. At the same time, the Sino-U.S. nuclear relationship has become more relevant. This is a more serious issue for Japan’s national security than U.S.-Russia relations, because the Far East in the Cold War was the second front, but East Asia could now be the first front. In addition to this geostrategic standpoint, with its significant efforts to develop conventional anti-access/area-denial (A2/AD) capability, China is challenging U.S. superiority with air and maritime forces in the Western Pacific.

Under such strategic conditions, Japan’s strategist community pays more attention to strategic stability. The main focus for them is crisis stability, or, more precisely, mutual vulnerability. The author, for example, raises the issue of the stability-instability paradox, focusing on mutual vulnerability in strategic stability and pointing out that U.S. acceptance of a condition of mutual vulnerability between the two countries could cause deterioration in the regional security environment through that paradox.6 The stability-instability paradox implies a situation in which mutual deterrence at the strategic level leads to a challenger’s aggressive behavior at the regional level, because that challenger perceives that the counterpart would refrain from responding to avoid escalation. Japan’s strategist community demonstrates serious concern that this paradox could be realized in this way: in the event that the United States explicitly accepts mutual vulnerability with China, China may make even bolder moves, with the attendant risk of escalation, from the gray zone to conventional conflict. These moves might be based on China’s overconfidence in its deterrence against a U.S. response and its assessment that the United States would want to avoid a severe showdown at the strategic nuclear level because of mutual vulnerability. In this way, crisis stability based on mutual vulnerability at the strategic level may invite instability at the theater level.

Ishikawa Taku, another nuclear strategist in Japan, points out the asymmetry in vulnerability within this region.7 While China and North Korea have acquired invulnerable theater strike capabilities with road-mobile missiles, Japan, South Korea, and Taiwan lack such strike capability. In this sense, China and North Korea enjoy one-sided invulnerability. Ishikawa argues that this asymmetrical invulnerability is offset by U.S. theater and strategic strike capabilities, which hold China and North Korea’s full range of targets at risk. With its commitment to extended deterrence, the United States guarantees regional mutual vulnerability even though regional allies and friends lack strike capability.

This implies that regional allies and friends might be highly sensitive to the fear of de-coupling, because their one-sided vulnerability can only be mitigated and resolved by the assistance of the United States. Even worse, in the face of China’s rapid development of theater-level A2/AD capabilities, the United States’ in-theater strike force may be easily neutralized once actual kinetic conflict breaks out. Again, this observation reaffirms the seriousness of Japanese concern about the stability-instability paradox if the United States admits mutual vulnerability at the strategic level.

As these two analyses reveal, Japan’s focus on strategic stability in the twenty-first century can be characterized as a regional emphasis. The Japanese treat theater-level strategic stability and strategic-nuclear-level strategic stability as if they are two separate layers. They do not see how strategic stability at the strategic nuclear level can cover all regional security potentials that lead to instability. Ishikawa treats theater-level strategic stability as separate from the strategic nuclear level, and the author has applied negative implications of strategic stability at the strategic level to a situation at the theater level. This demonstrates the necessity of integrating analysis between the strategic and theater levels to redefine the concept of strategic stability.

In addition, Japan’s strategists cover arms race stability. They especially point out that the current lack of transparency concerning China’s nuclear arsenal threatens the stability of the arms race.8 With a lack of credible sources of nuclear doctrine and force structure, incentives for nuclear expansion on the other side would not decrease.

In short, Japan’s view on strategic stability between the United States and China is skeptical in terms of whether it brings stability to the regional strategic situation. Rather, they are concerned that it may undermine regional stability.

Challenges to Redefining Strategic Stability in the Regional Context

Strategic stability is a concept developed in the Cold War between two nuclear superpowers fiercely competing with each other, in an era when the extinction of humankind in an all-out nuclear war was a realistic worst-case scenario. Faced with the differences between the bipolar Cold War world order and the current multipolar one, as well as between the U.S.-Soviet ideology-based rivalry and the potential U.S.-China strategic competition, the traditional concept of strategic stability will have to undergo some change if it is to remain relevant. To redefine or reformulate the concept of strategic stability requires dealing with three challenges.

Defining Mutual Vulnerability

This is the first challenge. Mutual vulnerability is a key concept for crisis stability because no party will have first strike incentive if all parties are vulnerable to the others’ second strike capability. To hold the other parties at risk, all parties must have invulnerable strike capabilities against some others’ potential first strike. If country A’s strategic strike capability is vulnerable to first strike, country B would have an incentive to launch a first strike to disarm country A. However, if country A’s strategic strike capability is invulnerable to country B’s first strike and country A can surely retaliate, there is no first strike advantage for country B, and vice versa. This situation is a classical definition of crisis stability based on mutual vulnerability.

This argument, however, fails to address the important question of how much second strike capability is enough for mutual vulnerability. This is actually an open question, especially since the Cold War. During the Cold War, there were no doubts between the United States and the Soviet Union because of the clear concept of mutual assured destruction (MAD) involving the requirement for second strike capability. “Assured destruction” capability was considered to constitute vulnerability. Of course, assured destruction capability lacks quantitative rigor. It is intuitively clear, though, that it means possessing more than hundreds of warheads. Compared to the Americans’ and Soviets’ literally assured destruction capabilities, China’s current arsenal of strategic nuclear force is considerably modest, estimated to be twenty to forty warheads. This is less than 1 percent of the level agreed (6,000 warheads) between the United States and the Soviet Union in the Strategic Arms Reduction Treaty. If the Soviet Union only had forty nuclear-tipped intercontinental ballistic missiles (ICBMs) during the Cold War, the United States would have perceived it as a greatly favorable strategic balance, with a one-sided assured destruction capability, and would have accepted that situation without hesitation. Based on this analogy, China’s current level of strategic nuclear force would not be considered to produce a mutually vulnerable situation.

In addition, if the United States accepts that tens of nuclear-tipped ICBMs would be enough to produce mutual vulnerability, two serious issues arise. The first is a question about alliance management. As described above, in the Cold War, mutual vulnerability was closely linked with the notion of mutual assured destruction and, related, assured destruction capability. If the United States treats tens of weapons—which would have been considered a favorable strategic situation during the Cold War—as a strategic nuclear arsenal, Asian allies would interpret that they are less valuable than European allies were in the Cold War.

The second issue is how to mitigate the negative implications for nonproliferation. If a proliferator perceives that 1,500 strategic nuclear warheads, about the same level as in the New Strategic Arms Reduction Treaty (START), are necessary for the United States to recognize mutual vulnerability with the other country, that proliferator would give up its development of such a strategic nuclear arsenal. If 200 are necessary, still that proliferator would be dissuaded. If twenty is enough, however, that can be achieved by some countries, especially North Korea and Iran. If the United States sets the bar of mutual vulnerability between twenty and forty warheads, it would give an achievable numerical target to countries that consider the United States a potential adversary. In this sense, recognizing mutual vulnerability with China under the current quantitative balance would incentivize regional challengers against the United States and would have negative implications for nonproliferation.

Theater Level Versus Strategic Level

Interactions between theater-level and strategic-level strategic stability represent the second challenge. As discussed, there are asymmetrical vulnerabilities in East Asia. With a rapid modernization of military force, especially concentrated efforts to develop A2/AD capabilities, China has acquired significant prompt and precise strike capabilities through ballistic and cruise missiles. By contrast, other countries in the region lack such capabilities for counterstrike. In addition, U.S. allies and friends in this region do not enjoy strategic depth with regards to opposing China. In this sense, U.S. air and maritime strike capabilities are essentially required to offset such an asymmetrical vulnerability.

At the same time, however, the main objective for China to develop A2/AD capability is to hold U.S. intervention forces at risk to restrain U.S. decisionmaking, or to physically block the U.S. reinforcements in this region. If China’s advanced A2/AD capabilities succeed in neutralizing U.S. ground-based tactical aircraft, sea-based tactical strike capabilities, and aircraft carriers, the United States would lose a significant part of its strike forces, and these forces would no longer offset strategic disadvantage in the theater. In this sense, China has first strike advantage in this region that the United States does not have, at least at theater level.

Under this situation at the theater level, strategic stability at the strategic level alone may bring significant harm for regional allies. Rather, it simply works to de-couple alliances and enhance the risk of the stability-instability paradox. Therefore, if one wants to redefine strategic stability in East Asia, it is necessary to think about how to guarantee strategic stability or, more precisely, mutual vulnerability at the theater level. Logically, if U.S. regional allies acquire prompt regional strike capabilities, that kind of situation can be realized. Or, setting aside the cost issue, if these countries deploy robust missile defense systems, the current one-sided vulnerability would be resolved and a mutual invulnerability situation would arise, resulting in a great improvement to regional level strategic stability. In short, the reformulation of strategic stability must be promoted in a way that integrates the theater level with the strategic level.

Arms Race Stability

The third challenge is about arms race stability. In addition to the transparency issue, Sino-U.S. strategic stability considerations would face more structural problems on arms race stability from Russia. During the Cold War, the participants in the nuclear arms race were realistically limited to just two players, the United States and the Soviet Union. Therefore, the game of interaction was very simple. If both parties had 1,000 warheads, numerical equality was achieved. Needless to say, asymmetrical conventional balance, different geographical locations with regards to Europe (a main front in the Cold War), and different nuclear force structures and doctrines made the problem complex, but the number of players for nuclear arms control and actors for strategic stability was limited to two.

Though the Sino-U.S. relationship is now considered to be the most important great power relationship, in terms of nuclear arms control Russia is still another key player for the United States, as the two countries agreed to 1,550 deployed warheads when signing New START. Therefore, Russia cannot be ignored.

After New START was concluded, some Japanese scholars believed that further reduction of nuclear warheads would require China’s participation. Creating a nuclear arms control regime with three players is not as simple as adding one country to existing arms control negotiations. In the case where countries A, B, and C are negotiating, they would face a serious conundrum in determining how many warheads would be appropriate. Each country needs to worry about the other two ganging up. Therefore, if the three countries deploy almost the same size of strategic nuclear arsenals, all three countries have incentives for arms expansion, rather than keeping the status quo or engaging in arms reduction. In short, this situation is completely deficient in arms race stability for structural reasons. This deficiency simply comes from the number of players and is highly difficult to resolve. If China continues its arms build-up and if it increases the size of its nuclear arsenal, or if the United States and Russia continue nuclear arms reduction, this difficult situation may be brought about. In thinking about strategic stability between the United States and China, this problem cannot be avoided.


Japan’s strategic community in the twenty-first century pays significant attention to the strategic stability issue by introducing the regional factor. Based on those thoughts, various challenges can be raised in addressing the reformulation of strategic stability. One should not forget that strategic stability is a highly technical debate about reducing first strike and arms race incentives by tailoring force structure. But designing and developing force structure is a part of statecraft. In the Cold War, the Anti-Ballistic Missile (ABM) treaty was a great symbol of the era’s strategic stability debate.

In 2001, after serious debate about missile defense, then U.S. president George W. Bush decided to withdraw from the ABM treaty and put forward the New Framework by declaring that Russia is no longer an enemy. In this post-MAD era, the role of technical written agreements regarding force structure appeared to be limited.9 Thus, political deliberation, including engagement with China, should coexist with the increase of deterrence through alliance strengthening, gray-zone crisis control, capacity building for regional friends, and a full range of efforts for crisis management. Debate about strategic stability is important, but one should not forget this is a part of—and in some ways complementary to—such broader deterrence efforts.

About the Author

Takahashi Sugio is a research fellow at Japan’s National Institute for Defense Studies and chief of its Policy Simulation Division.  He has published extensively in the areas of nuclear strategy, the Japan-U.S. alliance, and East Asian regional security.


1 M. Taylor Fravel and Evan S. Medeiros, “China’s Search for Assured Retaliation: The Evolution of Chinese Nuclear Strategy and Force Structure,” International Security 35, no. 2 (Fall 2000): 48–87; Fiona Cunningham and M. Taylor Fravel, “Assuring Assured Retaliation: China’s Nuclear Posture and U.S.-China Strategic Stability,” International Security 40, no. 2 (Fall 2015): 7–50.

2 Momoi Makoto and Kosaka Masataka eds., Takyokuka Jidai no Senryaku: Kaku Riron no Shiteki Tenkai [Strategy in a Multipolar Era: Historical Development of Nuclear Strategy] (Tokyo: Japan Institute for International Affairs, 1973).

3 The Japan Association of International Relations, Kokusai Kankei [International Relations] 90 (March 1989).

4 Ogawa Shin’ichi, Kaku: Gunbikanri Gunshuku no Yukue [Nuclear Weapon: Arms Control and Disarmament] (Tokyo: Ashi Shobo, 1996); Umemoto Tetsuya, Kaku Heiki to Kokusai Seiji [Nuclear Weapon and International Politics] (Tokyo: Japan Institute for International Affairs, 1996); Iwata Shuichiro, Kaku Senryaku to Gunbi Kanri: Nihon no Hikaku Seisaku no Kadai [Nuclear Strategy and Arms Control: Agenda for Japan’s No Nuclear Policy] (Tokyo: Japan Institute for International Affairs, 1996).

5 Ogawa Shin’ichi, “‘Kaku no Kasa’ no Rironteki Kento [Theoretical Analysis on ‘Nuclear Umbrella’],” Kokusai Seiji [International Relations] 90 (March 1989): 91–102.

6 Takahashi Sugio, “Kaku Heiki wo Meguru Shomondai to Nihon No Anzen Hosho: NPR-Shin START Taisei, ‘Kakuheiki no Nai Sekai,’ and Kakudai Yokushi” [Issues of Nuclear Weapon and Japan’s Security: NPR-New START Regime, ‘Nuclear Free World,’ and Extended Deterrence], Kaigai Jijo 58, nos. 7–8 (Summer 2010): 30–51.

7 Ishikawa Taku, “Hokutou Ajia ni Okeru ‘Senryakuteki Anteisei’ to Nichibei no Yokushi Taisei” [‘Strategic Stability’ in Northeast Asia and Deterrence Posture of the U.S. and Japan], Kaigai Jijo 61, no.3 (May 2013): 36–48.

8 Takahashi Sugio, “Nichibei Doumei ni Okeru Yokushi Taisei” [Deterrence Posture in the U.S.-Japan Alliance], Kaigai Jijo 61, no. 3 (May 2013): 85.

9 Takahashi Sugio, “Beikoku no Misairu Bouei Kousou to Posuto MAD no Kokusai Anzenhosho [U.S. Missile Defense and International Security in Post-MAD Era],” Kokusai Anzen Hosho 29, no.4 (March 2002): 1–18.