Introduction

An irony of the end of the Cold War was confirmation that it was, in fact, never cold in the first place. In the early 1990s, interviews with Soviet veterans and newly opened archives verified that Soviet pilots covertly participated in air-to-air combat with American pilots during the Korean War for two years. About a decade later, declassification of 1,300 American intelligence documents confirmed an even more striking fact: US intelligence agencies knew about the operation. One intelligence review from July 1952, a full year before the end of the war, estimated that 25,000–30,000 Soviet military personnel were "physically involved in the Korean War" and concluded that "a de facto air war exists over North Korea between the UN and the USSR." In short, the Cold War started hot. Yet neither Moscow nor Washington gave any public indication that direct combat was taking place.

This episode is a dramatic example of the two related phenomena this book seeks to understand. The Soviet entry in the Korean War is a case of covert military intervention, in which an external power secretly provides military assistance during a war. The American decision to stay silent after detecting Russian pilots is a case of collusion, in which one government detects but does not publicize or confirm the secret intervention of another government. The episode raises two related but distinct questions. First, why use a covert form of intervention, especially if it will be detected by an adversary? Second, why would an adversary play along?

The conspiracy of silence that emerged in the Korean War is but one example of a broader phenomenon. In political campaigns, rival candidates may uncover evidence of secret legal or ethical violations by their opponents. While going public with such information is tempting, exposure could force the rival candidate to respond in kind and lead to a rash of attack ads and inflammatory accusations. Such mudslinging could depress turnout and open the door for other candidates, creating good reason for mutual restraint regarding secrets. Childhood family dynamics also feature reciprocal secret keeping. Two siblings often know about one another's secrets, be it hidden Halloween candy, forged homework, or a clandestine romantic relationship. Exposing the other's secret to teachers or parents, while tempting, might prompt a reaction that neither sibling wants. If this scenario looms, then a sustainable conspiracy of silence could emerge. Finally, firms may find evidence that their competitor uses offshore bank accounts to evade taxes. The detecting firm may be tempted to expose and undermine its competitor's advantage. Yet doing so risks provoking regulators to more closely scrutinize the industry as a whole. One reasonable response would be mutual restraint in keeping secret such tax evasion.

In each example, a mutually unacceptable outcome influences both the initial act of secrecy and the response by one who finds the secret. The central insight is that mutual silence may result if individuals, firms, or governments can act secretly, observe one another doing so, and share fear of a mutually damaging outcome. Cooperative secrecy of this sort is not so surprising for siblings that live together or firms that might price fix or collude in other ways. However, such behavior is quite surprising in world politics, especially during war. That collusive secrecy would emerge among rivals under anarchy is especially unexpected.

This book analyzes the politics of secrecy in war and puzzling features like tacit collusion among adversaries. Secrecy has long been a hallmark of international politics where "incentives to misrepresent" can be powerful for governments that must fend for themselves. Seeing states act covertly is not surprising per se. After all, secrecy can be essential for protecting military forces in the field and for operational surprise. Hence the adages that "loose lips sink ships" and "tittle tattle lost the battle." Yet secrecy in the Korean War example appears to be serving different ends. Covert activity was observable to the rival. Rather than being in the dark, Moscow's adversary had a unique window into its covert behavior. Moreover, secrecy in this case seems to have been mutually beneficial. Both the American and the Soviet leaders appeared to derive value from keeping the public and other governments in the dark.

This book links such decisions to limited war dynamics and the desire for escalation control. Large-scale conflict escalation is a mutually damaging outcome that is influenced by exposure decisions. I develop a theory in which initial covertness and reactive secrecy are driven by the need to control escalation and avoid large-scale conflict. When escalation risks are significant, adversaries will tend to share an interest in prioritizing control. External military involvement in a local war raises the prospect of expansion in scope and scale. Intervening covertly, however, allows both the intervener and its rivals to better control what scenario unfolds following the intervention. Keeping an intervention covert — that is, acting on the "backstage" rather than the "frontstage" — has two limited-war benefits: easing constraints from a domestic audience and improving communication about interest in limited war. Covertness minimizes domestic hawkish pressures and expresses a mix of resolve and restraint that supports limited war. In the Korean War, covertness regarding the Soviet role allowed each side to operate with fewer constraints, to save face as it limited war, and to have confidence that its adversary valued limiting the conflict. This happened because of, rather than in spite of, detection by the other side. A central finding of the book is that this is not one-of-a-kind. Rather, covertness and collusion are an important part of wars ranging from the Spanish Civil War in the 1930s to the American occupation of Iraq in the 2000s.

Beyond developing a novel logic for secrecy in war, this book also offers new insights into the very nature of modern war. In the wake of two devastating world wars in the first half of the twentieth century, how did great powers avoid a third? Nuclear weapons, democracy, and bipolarity are typical answers. This book provides a different take on this question. As O'Brien notes, wars still erupted after 1945 despite these larger changes but were "guided by the principle that the conflict should be geographically limited to the immediate overt belligerents." I show that leaders learned over time to use covertness and collusion to avoid domestic constraints and miscommunication that might otherwise lead to large-scale escalation. This book underscores that overtness is an important qualification and identifies how it came to be. Conflicts like the Korean and Vietnam Wars featured direct casualties among the major powers on the backstage. Moreover, understanding these historical links between limited war and secrecy...