Preventive War

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Preventive war occurs when a state launches a military conflict to prevent another state or other international actor from becoming a threat. This type of war differs from the more typical situation in which states go to war after a period of crisis or as a reaction to a particular event. Preventive wars are not in response to a specific crisis or direct threat to security, but rather to a perception of a potential change in the future balance of power between a state and its likely adversaries. Preventive war differs as well from preemptive war, in which a state attacks in order to disrupt an enemy about to attack first. The difference between prevention and preemption is often a blurred one, but preemption always occurs just before the outbreak of hostilities and is directed against an enemy clearly in the process of preparing an attack, whereas prevention can occur during times of relative peace.

Although preventive war is a fairly rare path to war, there are nonetheless many examples of it throughout history. The Second Peloponnesian War of 431–404 b.c.e., between the Greek city-states of Athens and Sparta, took place after many years of tension and hostility between the two great rivals. When war broke out, however, it was not because of any issues that directly pitted Athens and Sparta against each other. Rather, the Spartans had come to feel it was now or never—they would have to go to war before Athens became undefeatable. As the writer Thucydides noted in his history of the war, the actual issues between the two city-states were only proximate causes of war, whereas the true source of the decision to go to war was Sparta's fear of "the rising power of Athens." In this case, neither Athens nor Sparta was directly threatened by the other at the moment hostilities broke out. The Spartans elected to go to war anyway out of a fear that Athenian power would one day overwhelm them if they chose otherwise.

Another example of preventive war was the Japanese attack on the United States in 1941. The Japanese, who were engaged in a major war in China at that moment, were suffering from an American embargo of important raw materials. Japanese concern that America was going to grow powerful enough to thwart Japanese designs for dominating the Western Pacific region led to a decision to remove the United States as a potential naval competitor. Aside from the embargo, which could be considered an important reason to go to war, there was no direct American military threat to Japan. The Japanese nonetheless acted to prevent any such threat from arising.

During the early period of the Cold War, in the late 1940s and early 1950s, some Western leaders and thinkers called for preventive war against the Soviet Union. Until 1949 the United States held a monopoly on nuclear weapons; as it became clear that the Soviets were soon to have such weapons of their own, there was considerable fear that it would later become impossible to contain them militarily. These calls for preventive war, however, were few in number, and became irrelevant once the Soviets developed nuclear arms.

One of the most controversial examples of preventive war took place in 2003, when the United States led a coalition to war against Iraq on the grounds that Saddam Hussein's regime continued to work on developing weapons of mass destruction (WMD), including nuclear weapons. This decision to go to war was in keeping with what some observers believe is a new American doctrine of preventive war (sometimes referred to as the "Bush Doctrine.") It states that the United States must act to forestall threats, from both state and non-state actors (such as terrorists), particularly because of the possible use by such groups of WMD. Although many countries agreed with the U.S. action in Iraq as a justifiable response to a threat, other nations condemned the concept of preventive war in principle, regardless of the supposed threat. That debate is likely to continue for many years.


Brodie, Bernard. Strategy in the Missile Age. Princeton, NJ: Princeton University Press, 1959.

Trachtenberg, Marc. History and Strategy. Princeton, NJ: Princeton University Press, 1991.

Thomas M. Nichols

See also:Preemptive War.

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Preventive War

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