The forthcoming article “The logic of secret alliances” by Peter Bils and Bradley C. Smith is summarized by the author(s) below.
A primary goal of military alliances is to deter aggression from enemies. Traditionally, alliances are understood to achieve this goal by serving as a costly signal of members’ commitment to fight alongside one another against a shared enemy. By observing allies engage in costly action such as policy coordination or the provision of military equipment, enemies infer that only states seriously committed to each other’s defense would bear these costs. Through this logic, alliances alter the calculus of deterrence and reduce an enemy’s incentive to attack.
In light of this signaling logic, secret alliances stand out as odd. For the signaling mechanism to operate, it is self-evident that an alliance, and the costs imposed by it, must be visible to adversaries. This presents a puzzle: if a primary goal of alliances is to deter enemies through signaling, then why would allies keep their commitments to one another secret?
In this paper, we argue that secret alliances are an attractive option when the alliance may act as a signal of members’ alignment. In our theory, alliances play two roles. First, they aggregate capabilities, allowing members to better resist aggression from a shared enemy. Second, and importantly for our argument, the presence of an alliance may endogenously reveal information about the constellation of interests in the international system. Consequently, a new alliance can indicate that a state previously thought to be friendly is, in reality, an adversary. We argue that if there is significant uncertainty about the alignment of states’ interests then the second effect dominates and secret alliances emerge.
To develop this argument, we analyze a formal model in which states may enter into secret or public alliance agreements. We find that if there is uncertainty about the alignment of interests then secret alliances occur in equilibrium. We also find that secret alliances have general effects on deterrence, undermining the deterrent value of concurrent public alliances.
Our theory explains variation in the prevalence of secret alliances over time. Prior to World War I secret alliances were the norm. However, by the Cold War era they are virtually non-existent. Our model points to the emergence of two phenomena after World War II to explain this pattern. First, the movement of the international system from a multipolar to bipolar environment reduced uncertainty about states’ alignments. Second, the advent of nuclear weapons significantly increased the deterrent value of alliances, further mitigating the need for states to maintain secrecy about their alignments.
About the Author(s): Peter Bils is an Assistant Professor of Political Science and Economics at Vanderbilt University and Bradley C. Smith is an Assistant Professor in the Department of Political Science at Vanderbilt University. Their research “The logic of secret alliances” is now available in Early View and will appear in a forthcoming issue of the American Journal of Political Science.