When Are Arms Races Dangerous? Rational versus Suboptimal Arming

Are arms races dangerous? This basic international relations question has received extensive attention.¹ A large quantitative empirical literature addresses the consequences of arms races by focusing on whether they correlate with war, but remains divided on the answer.² The theoretical literature falls into opposing camps: (1)arms races are driven by the security dilemma, are explained by the rational spiral model, and decrease security, or (2) arms races are driven by revisionist adversaries, explained by the deterrence model, and increase security.³ These theories support divergent policy guidance—arms control versus arms competition.⁴ Neither body of literature, however, succeeds in isolating the causal impact of building arms.

To solve this problem, this article proposes a new perspective for assessing the consequences of arms races.⁵ Scholars need to ask whether an arms build-up was a state's best option for achieving its goals—security and possibly other vital interests. I argue that a sharp distinction must first be made between a state's international security environment and its decision to build arms. If a state's security environment necessitates an arms buildup, then arming, as well as the competition that ensues if its adversary responds, is rational and the state's best policy option. Even if arms races correlate with war, they do not cause it. Instead, the state's security environment causes the arms race and in turn war. In contrast, if the state's decision to launch a buildup is poorly matched to its security environment, then the military buildup and the arms race that it provokes reduce the state's security. It is these suboptimal races that are dangerous—that is, they make war unnecessarily likely.

To implement this approach, I address two questions. First, under what conditions is an arms buildup a state's best option? Second, have states engaged in arms races when they should not have? The response to the first question provides a rational baseline that is necessary for answering the second question. I develop a strategic choice theory of when a rational state should build up arms instead of pursuing restraint and cooperation. A state's arming policy reflects its own motives and the constraints and opportunities created by its security environment. The security environment is determined by material variables—power and the offense-defense balance—and by information variables, with the most important being the state's information about its adversary's motives and goals. The theory draws on defensive realism, but is more general, addressing variation in information about motives, and the decisions of greedy states, as well as the decisions of security seekers. Using this theory to evaluate many of the past century's key arms races, as well as cases of cooperation, I find that a number of these races were suboptimal.

Reformulating the question of arms race consequences clarifies a serious problem with the quantitative literature by explaining why correlation might not reflect causation. In addition, it advances the theoretical debate between the spiral and deterrence model explanations by focusing on the distinction between rational and suboptimal competition. The spiral model, like the deterrence model, offers a rational explanation for arms buildups. These races may be tragic, occurring between states that lack fundamental conflicts of interest, but arms buildups are nevertheless each state's best option for security. In these cases, the international environment, not the arms race, is the real source of danger.

The article first explores the rationale for reformulating the arms race question and identifies a number of significant implications for studying the consequences of arms races. The second section develops the strategic choice theory of arming. The third section applies the theory to assess states' arming decisions. The final section briefly explores policy implications for the United States. Current U.S. policy anticipates the rise of powerful adversaries. The 2002 National Security Strategy calls for maintaining forces strong enough to dissuade military...