Almost immediately upon its 1977 publication, Michael Walzer’s Just and Unjust Wars became the most influential modern work on the laws of war. Though written by an avowed anti-war activist who opposed Vietnam, the work won popularity and praise because it rejected both amoral realism and pacifism and sought to resuscitate the tradition of just war. It did not bore with complex theories of rights and justice, but instead tried to find common ground by thinking through actual historical examples: WWII strategic bombing; Nagasaki and Hiroshima; the 1967 Six-Day War; and nuclear deterrence. The book’s influence is such that political leaders and opinionmakers seem to seek out Walzer’s blessing every time the United States launches a war.

Students of military history might not see much new on the surface of Just and Unjust Wars. He defends the idea of Just War, and more specifically the separation of jus ad bellum (the legality of beginning a war) from jus in bello (the legality of the means of fighting). A WWII German solider, for example, can legally participate in a conflict, and thus receive immunity for killing Allied soldiers in combat, even though Nazi Germany committed illegal aggression by starting the war. To take the flip side, Walzer also argued that a nation could be engaged in a just war, such as the U.S. defending NATO from a Soviet invasion, but still fight illegally by using nuclear weapons against cities. He defended the age-old principle of noncombatant immunity, which requires that nations not intentionally target civilian populations and property, against both realists and utilitarians who argue that nations should resort to such measures if they can bring war to a quicker end.

Walzer called these set of rules the “War Convention.” Uniquely, for its time, Just and Unjust Wars proceeded to test these principles against a series of well-known historical cases. Some of his conclusions do not surprise: he found that nations could use force in their own self-defense and the defense of other nations. Others do: he concluded that Israel’s 1967 preemptive first strike against the Arab nations was morally legitimate. Yet others even seem irresponsible: he argued that the United States could not rely on mutually assured destruction to counter the Soviet Union because it would be immoral to launch a retaliatory nuclear strike. Walzer would not have dropped the atomic bomb on Hiroshima and Nagasaki, even though allied leaders estimated that an invasion of the Japanese home islands would have resulted in one million allied casualties and eight million Japanese—far less than the lives lost in the nuclear attacks. Nevertheless, by focusing on historical and practical examples, Just and Unjust Wars created a common arena within which philosophers, the military, and politicians could argue about war.

Despite its welcome emphasis on historical examples, Just and Unjust War may leave the military scholar wanting in its conception of political theory. Just and Unjust War contributed to philosophy by replacing the foundations of Just War Theory, which had long rested on natural law (see the earlier discussions in this series on Cicero and Grotius), with the liberal approach of understanding politics in terms of individual rights. In Walzer’s view, individuals in war retain their right to life and liberty, but lose it when they choose to bear arms in war; killing in war becomes legitimate against combatants, therefore, but not civilians who do not choose to fight. Nations too have rights, that of territorial integrity and political independence, and can legally and morally defend themselves against aggression by others.

But Just and Unjust Wars did not fully develop a convincing theory that explains why individuals in one nation must respect the rights of individuals in another nation. The modern liberal theory of individual rights rests on the idea of social contract. Individuals leave the state of nature and enter into a shared society with others for their mutual security and benefit, and concede some of their rights to society in exchange. But as Hobbes first argued, the social contract is between individuals of the same political community. Without a supranational government with enforcement authority, there could be no rules that applied between nations. If nations represent different social contracts between different peoples, Just and Unjust Wars does not persuasively explain why nations must follow a common morality between themselves.

Nor does Just and Unjust Wars develop a theory that persuasively rejects utilitarianism. We can understand the arguments of military leaders and thinkers such as von Clausewitz or William Tecumseh Sherman, or of civilian leaders such as Winston Churchill or President Harry Truman, as the application of cost-benefit analysis to the battlefield. They might have pursued harsh, even brutal, methods in war—Sherman’s March to the Sea, Churchill’s demand for the strategic bombing of German cities, Truman’s use of atomic weapons—but they would argue that by bringing war to a faster close, the welfare benefits of their methods outweighed the harms of a prolonged conflict. As I argue in my recent book, Striking Power, modern military technology may make this choice even more acute. Technology provides the United States with the ability to inflict harms—such as shutting down a stock exchange; interrupting internet access; or paralyzing transportation networks—by targeting civilian property, but without causing civilian casualties. Just and Unjust Wars may not provide answers to these future questions, but it deserves a close reading as the common ground for our coming efforts to answer them.

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