U.S. security guarantees are extraordinary and complex commitments. The United States puts at risk its deployed forces and personnel, and potentially its homeland, for the sake of shared interests with allies. While the benefits of each alliance are unique, they provide the United States with security and economic partners that help to maintain international stability, promote economic growth and trade, and protect liberal values. But in extending deterrence to cover allies, the United States also increases its likelihood of being drawn into an unwanted war. As a result, the United States must sometimes deter its allies from undertaking certain actions and, conversely, assure its adversaries that it will behave in a measured manner. Plainly, it must balance assurance and deterrence both among and between its allies and potential adversaries.
To help inform U.S. policy choices, this article unpacks U.S. deterrence and assurance challenges. It begins with a discussion of U.S. extended deterrence of adversaries and assurance of allies along with an introduction of a Pacific Forum CSIS table-top exercise involving a Korean peninsula scenario. Then, drawing on the exercise and other historical examples, it shows why and how, somewhat counter intuitively, the United States deters allies and assures adversaries. In the third section, the article examines U.S. deterrence and assurance of both its allies and adversaries in the current security environment, highlighting the inherent problems that this creates among allies, among adversaries, and between allies and adversaries.
Deterring Adversaries and Assuring Allies
The United States maintains a network of alliances around the globe, each with unique characteristics. Yet central to each alliance is a robust military relationship and a commitment to mutual defense, with the United States as the more powerful state taking on a greater share of the defense burden. Washington honors its security guarantees to allies by committing its nuclear and conventional forces to deterring adversaries from attacking its allies and assuring allies that the United States will defend them if they are attacked. U.S. extended deterrence relies on a combination of capability and will. But most important, the effectiveness of extended deterrence and assurance depend on the perception of adversaries and allies respectively.
The fundamentals of extended deterrence and assurance were demonstrated at a track-1.5 table-top exercise that the Pacific Forum CSIS ran in Maui, Hawaii in July 2014. The exercise featured teams of U.S., Japanese and South Korean nationals from academia, think tanks, government and the military managing an escalating crisis on the Korean Peninsula. It began with the sinking of a Japanese vessel by North Korea in the Sea of Japan/East Sea, leading all three teams to recommend that the United States, with logistical support from Japan, strike the North Korean naval base that supported the attack. The U.S. team acted out of concern for Japan’s security, the credibility of the U.S.-Japan alliance and, by extension, the credibility of the entire U.S. alliance system. In the second move, North Korea retaliated with an artillery barrage against South Korean farmland north of Seoul (killing several people) and a nuclear detonation over the Sea of Japan/East Sea (with no initial casualties). While the U.S., Japanese and South Korean teams disagreed over how to respond, many felt that the United States needed to put an end to North Korea’s active nuclear weapons and long-range missiles. The U.S. team, in line with the 2014 U.S. Quadrennial Defense Review , felt it could not allow Pyongyang to “escalate [its] way out of failed conventional aggression.” It was also motivated by a desire to hold North Korea accountable for breaking the nuclear taboo and to send a message to other states that future nuclear use would have severe consequences.
The responses of the U.S., Japanese and Korean teams were somewhat predictable and in line with common understandings of extended deterrence and assurance. But the Maui exercise also exemplified that, at times, the United States seeks to discourage, or deter, actions by its allies and, conversely, assure its adversaries. U.S. efforts to deter allies and assure adversaries should not be surprising. Deterrence—the act of using fear of consequences or punishment to change a country’s calculus and inhibit behavior—has been a key feature of alliance relationships, just as assurance—the act of using declarations or guarantees to inspire confidence in how a country will act in particular circumstances—has been central to adversary relationships. But in the twenty-first century, more so than during the Cold War, the United States faces increasingly complex challenges in managing its alliance and adversary relationships.
Deterrence in Alliance Relationships
Elements of deterrence have long been discussed as a key component of alliance relationships. In his study of alliances during the 1815-1945 period, Paul Schroeder concludes that alliances are not only “weapons of power,” but also “tools of management” or, as he puts it, “ pactum de contrahendo” (pacts of restraint). But the deterrence factor in alliance relationships was perhaps best captured by nineteenth-century Prussian statesman Otto von Bismarck who, after allying his country with Austria to stop Vienna’s provocative policies toward Russia and prevent a major war, famously remarked that in every alliance “there is always a horse and a rider.”