As the Obama administration mulls over a list of potential steps to take on nuclear policy in its final months, discussion is sure to center on how these changes will affect US allies. Reports from Tokyo sand other capitals indicate that allies are already weighing in against one of the options, a declaration that the United States would not use nuclear weapons first in a conflict.
More and more, debates over US nuclear policy are not just about deterring adversaries but also about assuring allies of US security commitments. Over the course of the Obama administration, geopolitical events have not only made extended deterrence more difficult, but also, by extension, have made assurance of allies more difficult as well. It’s time to rethink how best to reassure allies of America’s security commitments, and refocus debate on deterrence of adversaries.
The US alliance network extends across the globe, defending free people against war and helping to prevent dangerous regional arms races. The United States also extends nuclear deterrence to select allies, including Japan, South Korea, and members of NATO. Russia’s invasion of Ukraine and its continued provocation against NATO countries, China's expanding territorial claims in the South China Sea, and North Korean hostility have all set off alarms in the capitals of US allies.
Drawing the line between threats that require a military response and those that can be addressed through other means can be difficult, both for the Pentagon and for any alliance of nations. If Washington is not willing to fight a war over a small cyberattack or South China Sea land reclamation projects, it can cause anxiety in allied capitals about the credibility of American commitments. If differences of opinion persist within an alliance, the US ally may decide to rely on it less for defense needs, and instead adopt policies that the United States considers ineffective, disadvantageous, or dangerous—ranging from more assertive military measures to appeasement of a powerful aggressor. Many officials believe, as US Deputy Secretary of State Tony Blinken said in June, that if allies lose confidence in the US nuclear umbrella, they could decide to develop nuclear weapons of their own.
The Obama administration has devoted considerable time and attention to reassuring allies in Europe and Asia. In its 2017 budget, the Pentagon more than quadrupled its request for the European Reassurance Initiative. By the end of 2017, under this initiative, the US Army plans to have three Brigade Combat Teams continuously deployed in the region and equipment prepositioned for one more, plus provide allies with reinforcements in the form of aviation assets, special operations forces, and intelligence capabilities. In Asia, US defense officials have launched new dialogues on nuclear deterrence issues with Japan and South Korea. At periods of heightened tension, the Obama administration has repeatedly dispatched nuclear-capable bombers to fly over South Korea and other allies as a symbolic reminder of its nuclear guarantee. In both Europe and Asia, major joint exercises have helped teach allied militaries to work together to resist an attack and signal their ability to do so to potential adversaries. These joint exercises constitute a significant and under-recognized accomplishment, and will ensure that Obama’s successor inherits strong relationships.
For all the attention it has received, though, assurance is not very well understood. In general, deterrence and assurance are two sides of the same coin. A mission designed to deter an adversary also has the effect of assuring an ally of its security. Ideally, the equation works the other way too: Steps that allies request for assurance also deter an adversary.
Yet the two ideas are not conceptually or practically equivalent. Brad Roberts, who helped to manage nuclear alliances during his time in the Pentagon, writes eloquently in his recent book about the importance and difficulty of assuring allies today. He notes that in the years of the Cold War, “a conventional wisdom emerged that the standards for deterrence and assurance are very different.” In 1989, then-British Defense Minister Dennis Healey estimated that “it takes only five percent credibility of American retaliation to deter the Russians, but ninety-five percent credibility to reassure the Europeans”—because if the United States reneged on its alliance commitments, Europe stood to lose a great deal more than the Soviets stood to gain.
Today, as extended deterrence takes on new importance and allies reach out for assurance, the concepts are again diverging. US officials now discuss the need to meet not only the deterrence requirements of allies but also their “assurance requirements.” The new moves under the European Reassurance Initiative, US officials have said, will help the US European Command “transition from reassurance to deterrence.”
In principle, an ally should feel assured of its security when the partners act together to deter an adversary. Sometimes, however, US alliance partners ask for and receive new measures that appear to be only tangentially connected to deterrence. For example, most observers agree that US overflights of South Korea with nuclear-capable bombers do little to deter North Korea, and some believe they exacerbate crises unnecessarily. Similarly, the United States is pressing ahead with new missile defense sites in Romania and Poland, a decision for which Russia has promised to retaliate. Originally planned to hedge against a nuclear Iran, the sites ostensibly continue as a way of defending against Iran’s conventional missiles. Such actions may make US allies feel valued for a short time, but these kinds of assurance operations do not necessarily translate into an improved deterrence position.
There are five reasons it can be problematic to focus on assurance.
First, as deterrence becomes more difficult, it will simply not be possible to meet the Healey ratio. As his remark suggests, as deterrence requirements rise, assurance requirements will increase at a disproportionate rate. With force structure and posture increasingly constrained by budgetary politics in the United States and debates over the extent of nuclear modernization, it will not be sustainable to rely on new procurement and deployments to assure allies each time an adversary acts up.
Second, new assurance missions can send inflammatory signals to adversaries without having a real deterrent effect. Allies tend to request visible or symbolic demonstrations of the US commitment, which can further alarm an adversary without providing new deterrent leverage, as with European missile defense and Korean overflights. If an adversary takes new steps to respond, it can lead to new assurance requests, and a downward spiral of insecurity—even if deterrence was in place all along.
Third, some assurance relationships tend to privilege nuclear signals as more credible than conventional capabilities. However, US nuclear policy is a precise and highly constrained domain: Any new nuclear capability or deployment will have enormous ramifications for nonproliferation and stability, so US officials are limited in what they can do on this front. There will be limits to the Pentagon's ability to posture nuclear systems for assurance purposes.
Fourth, assurance requirements can be used by parts of a bureaucracy to push their preferences about US force structure. In 2009, four Japanese diplomats apparently presented testimony to a US commission on nuclear policy asking the Pentagon to redeploy nuclear cruise missiles on its submarines, a system that had been withdrawn in 1990. Japan’s Foreign Minister later clarified that his government did not take official positions on specific US weapons systems, but rumors persisted in Washington that these missiles were “Japan’s weapon”—in part because some US officials wanted to retain the weapons. More recently, opponents of potential changes to US nuclear policy from within the US security establishment have claimed that allies disapprove of the moves under discussion, even in light of evidence to the contrary.
Fifth, a focus on assurance can send perverse signals to allies. Blinken’s remark that failed assurance could lead South Korea or Japan to develop nuclear weapons is hardly uncommon; the idea has appeared in the Nuclear Posture Review and official remarks, and has recently been discussed in depth in the Bulletin. Often, such statements seem designed to justify support for the alliance to domestic audiences in America. However, they only encourage the groups in South Korea and Japan that do want to go nuclear.
The next US president will have to devote considerable time and attention to establishing personal credibility with allies and carrying on the work of deterrence and assurance, especially after some reckless comments about allies made over the course of the 2016 presidential campaign. However, the next administration should also rethink how it conducts assurance in an age of increasingly complex asymmetric threats.
The United States and its allies should focus directly on the difficult challenge of deterring adversaries and defending against aggression. US officials should not treat assurance requests as categorical, but rather as signals that they should work with allies to set deterrence requirements and then meet them. As force structure and posture face new constraints, communication and security cooperation will become more important for reassurance. Allies should avoid symbolic displays of solidarity that do not help prevent conflict, and resist the temptation to request and offer new assurance steps as a way of “sending a message” in response to new provocations. Both US and allied officials should work to gain a clearer sense of the interests of their counterparts, and refrain from using assurance arguments to settle domestic disputes.
Allies should also not think of nuclear promises as inherently more credible than conventional-weapon assurances, or a signal of closer commitment, or a panacea for new challenges. Nuclear weapons are not well suited to deter or respond to grey-zone threats. The day-to-day joint missions of conventional forces to train, patrol, deter, and defend against provocations and war are not only a highly credible signal of America’s commitment to the security of its allies, they are also the most effective and important missions for the new generation of threats. Allies should value these routine but critical conventional operations and make new investments in areas like intelligence collection, readiness, special operations, and anti-submarine warfare.
Both sides should work to prioritize the difficult work of conventional deterrence that can keep allies safe—and not the nuclear systems that are better suited to avenging an ally after tragedy strikes. This is the best assurance that the United States can offer.
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