Conclusion

This concluding chapter provides an analytical summary of insights that emerge across the chapters, highlighting the ways in which the characteristics of different instruments of coercion examined in this book—nuclear weapons, operations on land, at sea, in the air, in space, and in cyberspace, and engineered migrations—can improve or undermine deterrence. By and large, the contributors to this book find that the notion of cross-domain deterrence is useful and can reveal novel insights that traditional deterrence theory obscures. Deterrence in history has often occurred across domains, combining land and naval power as well as force, diplomacy, and economic statecraft, but the logic of strategic choice has not been articulated. Deterrence theory as we know it may actually be a subset of cross-domain deterrence, an account of coercive bargaining that takes means as seriously as ends. Means matter because different tools and combinations of tools have different consequences for the costs, credibility, and consequences of deterrence. These insights opens up new research frontiers for international relations.

Beyond Military Deterrence

States interact in a multiplicity of domains, and most of them are not military in nature. Situating the security domain alongside economic and social domains of interaction among countries is important for creating a full analysis of a state’s priorities in a particular region, or with any particular other state. Failure to appreciate the nonmilitary dimensions of international relations in Asia in particular can lead one to misdiagnose the prospects of conflict and cooperation, potentially leading to tragic spirals. Data on East Asian defense spending over twenty-five years appears to present a puzzle: by many measures, East Asian military expenditures have declined significantly over the past quarter century. This finding appears starkly at odds with the conventional wisdom that Chinese bellicosity, its expenditure on anti-access/area-denial capabilities, and the United States’ reallocation of forces are increasing tensions in the region. Any policy of cross-domain deterrence that fails to appreciate interactions across the full multiplicity of domains of international intercourse risks courting deterrence failure.

Linkage Politics

Most discussions of cross-domain deterrence focus on variation in the means of coercion, but variation in political ends can be just as consequential. Cross-domain deterrence in the context of linkage politics, in which disparate political interests are tied together to create incentives for favorable outcomes, gives potential adversaries the opportunity to avoid confrontational meeting engagements by playing for time to clarify interests and choosing the means most suited to achieving new goals. A broader diplomatic conception of cross-domain deterrence can also highlight the potential of using financial, institutional, or other nonmilitary actions that render the threat or use of force less attractive. This chapter draws on newly available archival evidence to examine issue linkage politics in the context of changing strategic interests in the case of U.S. efforts to deter Soviet repression in Poland and East Germany at the end of the Cold War. In both cases, U.S. policymakers used diplomatic reassurance and threats of isolation to shape Soviet policy as the United States pressed its new-found political interests in Eastern Europe rather than its traditional preoccupation with military affairs.

Asymmetric Advantage

A widely held belief in deterrence theory, first articulated by Thomas Schelling, is that compellence is harder than deterrence. This chapter finds, however, that weak actors have often been able to successfully use coercive engineered migration to compel stronger states to alter their policies. The aims of coercive engineered migration vary tremendously and usually include political, military, and economic goals. Liberal democracies are especially vulnerable to this particular means of coercion, even as they have important advantages in other arenas. This novel example of compellence that relies on a nonmilitary form of cross-domain coercion shows very convincingly that a difference in means in the right context can have a major differential effect on the success or failure of coercion.

International Law and the Common Knowledge Requirements of Cross-Domain Deterrence

The complexity of cross-domain deterrence is a major barrier to establishing coordinated expectations about violations and consequences. For a system of cross-domain deterrence to work, actors must understand what actions will trigger a response, what the response is likely to be, and how willing the respondent is to act. Any such system is likely to be less robust than Cold War nuclear deterrence because of the number of domains involved, constraints on revealing secret capabilities or even the identity of the challenger, and a propensity for provocations that fall below the established threshold of response. This chapter recommends using an analogy to the law of war rather than to nuclear deterrence to understand the possibilities of setting up a workable regime of cross-domain deterrence, even as the author is pessimistic about the ability of any collective regime to adequately manage the complexity of cross-domain deterrence.

Cross-Domain Deterrence in American Foreign Policy

This chapter assesses the role of cross-domain deterrence in recent American foreign policy. Cross-domain deterrence is not a new phenomenon, even if our consciousness of it may be. Prominent cases from the Cold War, such as the Korean War and the Cuban Missile Crisis, can be interpreted through the lens of cross-domain deterrence and fruitfully compared with more contemporary cases, such as the Stuxnet attack on Iran. These cases illustrate the variation across domains by the adversary and U.S. responses. Considered together, the United States generally responded to these crises by initially limiting itself to the domain where a crisis started and only later expanding into other domains. The United States has typically been cautious when shifting domains and has tried to escalate in ways that would not produce adversarial retaliation.

Signaling with Secrets

How do you credibly communicate a threat that you cannot reveal? This problem is endemic for modern space and cyberspace capabilities, but the challenge of secrecy constraints in cross-domain deterrence is not a new phenomenon. During the late Cold War, nuclear forces deterred conventional attack, theater nuclear forces deterred strategic nuclear escalation, and conventional threats to nuclear capabilities deterred conventional attack. Some of these capabilities, particularly intelligence collection and electronic datalinks, depended on sensitive tactics and technologies that could not be revealed lest the enemy develop effective countermeasures. Secrecy created uncertainty about the true balance of power, which should have made conflict more likely, according to rationalist theory. This chapter shows, however, that the United States was able to use several mechanisms to communicate its capabilities to the Soviet Union without thoroughly compromising the ability to use them. Leveraging historical evidence from senior Soviet leadership, the chapter argues that U.S. nuclear counterforce strategy, which leveraged clandestine capabilities in many domains, nevertheless was effective in shaping Soviet perceptions and influencing Soviet policy.

Air Power versus Ground Forces

Classical deterrence concepts were developed to prevent nuclear war, for obvious reasons, and thus tend to focus on high-stakes crisis bargaining, or “chicken” games, to both threaten and avoid Armageddon. Yet deterrence may operate in many different settings (i.e., different games) and with repeated interactions by the players. Indeed, deterrence is prevalent, if underappreciated, at the operational level of war, even when a state is attacking at the strategic level. Drawing on a number of historical examples, this chapter argues that command of the air over the battlefield is operationally valuable because it deters ground forces from massing and maneuvering, which can benefit either offensive and defensive operations. The degree to which an air force can deter in war depends on various operational factors, including the degree of air superiority achieved over the battlefield, the capability of the air force to locate and target enemy ground forces, the composition of enemy forces, the presence of friendly ground forces, and permissive environmental conditions.

Deterrence in and through Cyberspace

Most of the discussion of cyber deterrence has been plagued by ambiguity and a lack of precedent, and this imprecision has resulted in vague or partially implemented policies. This chapter reviews debates about the definition of cyber operations and cyber deterrence, distinguishing the use of cyberspace to support deterrence in other domains and the deterrence of actions in cyberspace itself. The author finds that uncertainty is a resounding theme in this literature, which poses both challenges and opportunities for cross-domain deterrence. Cyber-enabled military capabilities might both bolster U.S. deterrence policies and incentivize attack. In cyber as well as in space, the United States confronts a difficult paradox of capability and vulnerability.

The Past and Future of Deterrence Theory

Renewed interest in deterrence today has been stimulated by the way recent efforts to sustain security and stability in international politics have often been unevenly successful or not successful at all. Efforts to deter, contain, and end conflict—whether terrorism, intrastate ethnic, religious and political fighting, and interstate fighting—have frequently run into difficulty. There is serious disarray in the East-West deterrence relationship once again, after a brief Cold War hiatus, with disturbing possibilities of outright conflict now being openly discussed among analysts and observers. Part of the reason that deterrence is so challenged today is that the very concept of deterrence—including cross-domain deterrence—has become seriously overstretched to apply to far more than it reasonably can, or should.