Following the nuclear revolution, the requirements for assurances among adversaries increased. When the United States and the Soviet Union realized after the Berlin and Cuban missile crises of the early 1960s that they had the power to destroy the planet, they devoted considerable time and energy to stabilizing their relationship. The operating model became nuclear deterrence, or the threat of massive destruction in retaliation for an act against one’s vital interests.

Nuclear deterrence required the two superpowers to simultaneously threaten and assure each other. As Thomas Schelling puts it, “the threat of massive destruction may deter an enemy only if there is a corresponding implicit promise of non-destruction in the event he complies.” Talking specifically about the role of assurance as an essential component of deterrence strategy, Schelling argues that, “To say, ‘One more step and I shoot,’ can be a deterrent threat only if accompanied by the implicit assurance, ‘And if you stop I won’t.’” Nuclear deterrence strategy also led the United States and the Soviet Union to maintain effective and survivable second-strike capabilities and, as a general rule, to assure each other that they would remain mutually vulnerable to nuclear retaliation. These assurances crystallized in various arms-control agreements and confidence-building measures, which regulated U.S. and Soviet nuclear capabilities and intentions and helped maintain a stable balance of terror, however imperfect it may have been, until the end of the Cold War.

The Maui exercise demonstrated the need for assurance of adversaries during a crisis. Each team attempted to provide “off-ramps”—de-escalatory options—to North Korea throughout the exercise. The U.S.-Japan response to North Korea’s initial aggression was decisive but proportional, suggesting that it was intended to be retaliatory, not escalatory. More important, while the U.S. team refused to let Pyongyang use nuclear weapons to terminate the conflict and recommended action to destroy North Korea’s nuclear arsenal, it stopped short of recommending regime change. Some even suggested a more limited strike that would hit key military targets without attempting to eradicate North Korea’s nuclear retaliatory capability. While fully recognizing the difficulty of signaling America’s limited intentions, participants tried to calibrate their response to assure Pyongyang that its survival would be guaranteed if it chose not to retaliate. This is consistent with U.S. Strategic Command’s Deterrence Operations Joint Operating Concept, which stresses the importance of considering the adversary’s “perception of the consequences of restraint or inaction”—that is, giving North Korea an exit to the crisis that Pyongyang can accept.

While assurance is common in adversary relationships, it is nevertheless different from assurance in alliance relationships. In both cases, the United States seeks to assure other countries that they can be confident about how the United States will act in particular circumstances. Yet, with allies, the United States often provides positive guarantees—promises to do something to address a problem—whereas adversaries are generally provided negative guarantees—commitments not to do something threatening.

 

Deterring and Assuring Allies and Adversaries in the Twenty-First Century

The United States continues to assure its adversaries even as it deters them, just as it deters its allies even as it assures them. In the current security environment, however, this task is more challenging because Washington adopts different approaches for different allies and adversaries.

 

Allies

In recent years, Washington has ramped up assurance of allies, mostly at their request. In Europe, this occurred in the context of NATO’s latest revision of its “Strategic Concept” in 2010 and its Deterrence and Defense Posture Review in 2012. In Northeast Asia, Washington used newly-established bilateral extended deterrence dialogues to assure Japan and South Korea.

But Washington has also sought to ensure appropriate burden sharing by encouraging its allies to better defend themselves. President Richard Nixon’s 1969 “Guam Doctrine,” for instance, emphasized that the United States “shall look to the nation directly threatened to assume the primary responsibility of providing the manpower for its defense.” Today, officials in Washington continue to believe that allies need to do more. There is an enduring disdain for free-riding and a growing realization that, in the current fiscally-constrained environment, the United States needs allies to more actively contribute to strengthening regional security architectures. The United States is, for example, working with Japan to strengthen its regional missile defense architecture by co-developing the Standard Missile-3 (SM-3) Block 2A interceptor. Seeing an opportunity for Japan to contribute even more, several Americans in Maui recommended that Japan develop its own long-range strike capability to respond to Korean Peninsula contingencies. They stressed that such capability would be particularly useful because the United States, under the terms of the U.S.-Russia Treaty on Intermediate-Range Nuclear Forces (INF Treaty), cannot legally deploy intermediate-range land-based missiles.

Yet while the United States encourages Japan—and its allies generally—to do more, it also seeks to maintain control. After recommending that Japan develop its own strike capability, the U.S. team cautioned that Japan should only use such a capability for coordinated actions within the framework of the U.S.-Japan alliance. While they wanted to encourage Tokyo to play a greater role in its own defense, Americans were equally eager to prevent Japanese actions that would increase the risk of U.S. entrapment. This frustrated Japanese participants, leading one to state that “sometimes it looks like you’re setting [Japan] up for failure, asking [Tokyo] to do more but not too much.”

The challenge for Washington is to properly manage expectations while avoiding mixed messages. The bilateral extended-deterrence dialogues established with Japan and South Korea in 2010 have made great strides in bringing Washington closer in sync with its Northeast Asian allies, but uncertainties remain. Managing expectations of allies is especially difficult because, in the current complex security environment, the United States has different expectations for different allies and regions. Allies do not fully understand why Washington expects actions by some that it denies to others.

U.S. expectations of European and Northeast Asian allies about extended nuclear deterrence, for example, differ considerably. In Europe, while the “supreme guarantee” of the security of NATO allies is provided by U.S., UK and French nuclear forces, the United States also forward-deploys nuclear weapons that it operates on dual-capable aircraft with its NATO allies. Moreover, the alliance’s nuclear roles and responsibilities are coordinated by the defense ministers of all member states, except France, in the Nuclear Planning Group. No such sharing arrangements exist in Northeast Asia, where extended nuclear deterrence is guaranteed by the U.S. nuclear triad of strategic delivery systems and the U.S. capability to forward-deploy nuclear weapons on bombers and fighter-bombers, should this become necessary. In other words, the Northeast Asian extended nuclear deterrence model relies solely on reach-back capabilities rather than forward-deployed systems.

Yet, as the Northeast Asian security environment deteriorates—with continued North Korean nuclear threats and increased Chinese assertiveness—experts in Japan and South Korea more frequently debate whether the U.S. nuclear umbrella in Asia should evolve toward an arrangement that more closely resembles the NATO model. At the official level, South Korea and Japan, at least thus far, simply want to better understand the NATO model and improve the respective bilateral extended-deterrence dialogues. But some influential people in South Korea, and to a far lesser extent Japan, have gone as far as calling for the development of independent nuclear weapons.

Washington also rejects the development of indigenous nuclear weapons by its allies. The Nuclear Posture Review Report makes clear that U.S. alliances, among other things, serve nonproliferation goals by acting as guarantees to non-nuclear allies that “their security interests can be protected without their own nuclear deterrent capabilities.” Implicit in this statement is that development of nuclear weapons by a U.S. ally would be a step too far and eliminate one of the important side benefits the alliance provides. The deterrence message is obvious: ‘develop nuclear weapons and you may be on your own.’

Proponents of nuclear weapons in South Korea and Japan note the tension in U.S. policy. While Washington currently forward-deploys nuclear weapons in Europe, it solely maintains the capability to do so in Asia, and this difference is likely to persist. In the wake of Russia’s intervention in Ukraine, even advocates of the withdrawal of U.S. nuclear weapons from Europe admit that it is unlikely to happen anytime soon. Rather, Nikolai Sokov and Miles Pomper suggest that “the debate will evolve in the opposite direction: some members of the alliance will insist on increasing reliance on nuclear weapons, while others will defend the status quo.” This debate, in fact, has already begun, with influential U.S. figures making a vigorous case against withdrawal and Polish anti-communist icon Lech Walesa arguing that Poland should “lease nuclear weapons” to ward off Russia.

Another important difference is that the United States works in tandem with two nuclear-armed states in Europe—the United Kingdom and France—to provide the supreme guarantee of NATO’s security, whereas it resists the development of nuclear weapons by its Asian allies. While the United Kingdom and France went nuclear before the conclusion of the Nuclear Nonproliferation Treaty (NPT), and thus did not violate international law, some in Seoul, Taipei and Tokyo may wonder if, when push comes to shove, the United States could accept a repeat of the European experience. Washington, however, continues to adamantly reject the development of nuclear weapons by any of its allies.