Just-war theory focuses on two issues: the justice of the decision to wage war and the justice of war conduct. About the war decision, just-war theorists require that decision makers have legal authority to wage war, that the cause to wage war be just, and that participants have a right intention. Just cause requires not only that the war be just in the sense of aiming to rectify a wrong, but also that the cause be proportionate to the death and destruction likely to result from the war. Just cause also requires that all reasonable means to avoid war have been exhausted, and that there be a reasonable hope of success. Since World War I, just-war theorists have allowed only national or collective self-defense as just cause for war.
For the criteria of war conduct, just-war theorists invoke two principles. The first is one of discrimination; namely, that just warriors should target only enemy personnel and property involved in waging the war. Thus the armed forces of the enemy and the production and transportation of war equipment are legitimate targets, but ordinary citizens are not. The second principle is one of proportion; namely, that just warriors should attack military targets only if the targets' importance is proportional to the collateral (unintended) death of ordinary citizens.
Allied bombing in World War II of residential areas of German cities raised serious just-war concerns about the targets. First, did the area bombing satisfy the principle of discrimination? Second, did such bombing, if sufficiently discriminate, satisfy the principle of proportionality?
Just-war theorists regarded the atomic bombing of Hiroshima and Nagasaki in 1945 as violations of the principle of discrimination. After the Soviets developed nuclear weapons, the United States adopted a counter-city strategy to deter a Soviet nuclear attack on itself or its allies. During the Cold War, just-war theorists objected that this strategy, which targeted Russian civilian populations, was contrary to the principle of discrimination. Some just-war theorists instead proposed a counterforce deterrence strategy. Other just-war theorists condemned all use of nuclear weapons as contrary to the principle of proportionality but allowed the threat of retaliatory use of nuclear weapons for deterrence.
From the late 1950s to 1965, the United States provided military and economic assistance to South Vietnam to suppress a communist insurgency supported by North Vietnam. From 1965 to 1973, the United States committed its own forces to the war. This triggered widespread popular dissent. There were just-war concerns on almost every count. There were claims the war was illegal, that the war had no just cause, or at least no proportionate just cause, and that the war conduct was indiscriminate or at least disproportionate. The dissent contributed significantly to the decision to end U.S. involvement.
America's involvement and wars in the Middle East have raised just-war concerns. Just-war theorists affirm the just cause of Israel to defend its people and pre-1967 territory but question some of its war conduct. Just-war theorists also affirm the right of Palestinians to their own state but condemn the targeting of ordinary Israeli citizens The U.S. decision to wage the Gulf War against Iraq in 1991 was challenged principally on geopolitical, economic, and personal-risk grounds, but some objected on just-war grounds, principally concerning the risk of disproportionate Iraqi civilian casualties. Renewed conflict between the United States and Iraq in 2003 raised broader just-war concerns about the legitimacy of a preemptive war without United Nations authorization and about proportionate just cause.
O'Brien, William V. The Conduct of Just and Limited War. New York: Praeger, 1981.
Regan, Richard J. Just War: Principles and Cases. Washington, D.C.: The Catholic University of America Press, 1996.
Walzer, Michael. Just and Unjust Wars: A Moral Argument with Historical Illustrations. New York: Basic Books, 1977.
Richard J. Regan