A Theory of the Laws of War

The laws of war govern the weapons and tactics that belligerents may use against each other. This paper uses a model of conflict to explain and evaluate the laws of war. In the model a nation’s propensity to engage in conflict is a positive function of the effectiveness of military technology, and a negative function of the destructiveness of technology. Accordingly, in theory nations would want to agree to laws of war that permit destructive weapons and tactics but limit their effectiveness. However, nations with different endowments and resources will enjoy differential advantages, and this makes agreement on specific laws of war very difficult. The paper discusses empirical implications of the argument, and discusses whether the Hague Conventions are consistent with the model. The ancient Greeks fought many wars among themselves but also observed rules of battle. These rules prohibited summary execution of prisoners, attack on noncombatants, the pursuit of defeated opponents beyond a limited duration. and many other forms of warfare that are condemned to the present day. Josiah Ober argues that the Greek rules were intended to limit the violence of war, and he, like many other historians, take comfort in what seems like a natural human tendency to limit the brutality of war. A war in which prisoners are spared is surely more humane than a war in which they are executed. But another interpretation is possible. These “rules” could be descriptions of behavioral regularities rather than constraints on self-interested behavior. Prisoners are not usually executed but only because they have value as hostages and are often ransomed. Armies often spare noncombatants because they pose no immediate threat, they can provide supplies, information, and other services, and armies do not wish 1 Professor of Law, University of Chicago. Thanks to Jack Goldsmith, Rich Hynes, and Richard Posner, and especially to Ryan Goodman and Derek Jinks, for helpful comments, to The Sarah Scaife Foundation Fund and The Lynde and Harry Bradley Foundation Fund for financial support, and to David Kitchen for valuable research assistance. 2 Josiah Ober, Classical Greek Times, in The Laws of War 13 (Michael Howard, et al. eds. 1994). to give other civilians a reason for resistance. And any army that pursues a defeated opponent risks outrunning its supply lines and falling into disorder. Patterns of behavior that seem humane are not necessarily signs of humanity. The view shared by Ober and others mistakenly assumes that the military objective is always to slaughter as many people as possible, when it is more often to acquire territory and secure other resources, activities that often are best accomplished by treating civilians and even enemy soldiers with restraint. The optimistic view about the laws of war is shared by many scholars in the international law community. Although their interpretation of events in past wars is, like Ober’s, often superficial—the common claim that international law prevented most belligerents from using poison gas against combatants during World War II makes an unnecessary puzzle of nations’ willingness to violate many other laws during that war— the pessimistic view that the laws of war have no effect is also too strong. It has trouble explaining why states talk as though they recognized laws of war, and in the last century made repeated efforts to codify them and expand them in treaties and conventions. The Hague Peace Conferences of 1899 and 1907 were the first significant official effort to spell out the rules of war. These rules included a general prohibition on weapons that cause “unnecessary suffering,” as well as several more specific restrictions on the use of weapons and tactics. Subsequent conventions have dealt with biological and antipersonnel weapons, the treatment of prisoners of war, and the treatment of civilians at time of war. And even though the laws of war were widely disregarded during World War I and World War II, they have been the subject of extensive diplomatic negotiation since 1945. The optimistic and pessimistic views, as fleshed out in the literature, differ in their assumptions about the motivations of states and their interpretations of evidence. The pessimists assume that states act in their interest, and their interest is usually that of security and power. The optimists assume that while states act in their interest, they also internalize the humanitarian norms reflected by international law, and treat them as 3 See Geoffrey Best, Humanity in Warfare (1980); Geoffrey Best, War and Law Since 1945 (1994).