A preemptive attack (or preemptive war) is waged in an attempt to repel or defeat an imminent offensive or invasion, or to gain a strategic advantage in an impending (usually unavoidable) war.

Preemptive war is often confused with the term preventive war. While the latter is generally considered to violate international law, and to fall short of the requirements of a just war, preemptive wars are more often argued to be justified or justifiable.

The intention with a preemptive strike is to gain the advantage of initiative and to harm the enemy at a moment of minimal protection, for instance while vulnerable during transport or mobilization.

While the labeling of an attack (on strategic and tactical levels) seldom is controversial, it is much more so in regard to the initiation of a war. For propagandist reasons, and in the name of information warfare, an adversary's defensive dispositions may often be attributed offensive purpose alleging the necessity of the own attack.

One hypothetical example of a preemptive war would be an attack staged against enemy troops, massed at a state's border, that were preparing to invade.

The Soviet Union's aerial attack on Finland on June 25, 1941, as an answer to the German attack on Russia of June 22 (Operation Barbarossa leading to the Great Patriotic War), can be argued to be an example of such an preemptive attack, although failed, and though the bombing of residential districts has to be attributed a psychological aim rather than a tactical. Finland's army was mobilized and prepared for both defense and offense, its government had declared its intention to remain outside of the war, and its parliament was assembled to confirm the status of nonbelligerence when attacked. The following Continuation War led to a three year long Finnish occupation of Russian Karelia.

Some commentators have pointed out that the Japanese attack on Pearl Harbor could be regarded as a preemptive attack.

It is the policy of the United States that preemptive war may be waged in appropriate circumstances. It is a part of the Bush doctrine and is supported by Senator John Kerry, 2004 Democratic nominee for the office of President of the United States.

See also

• Military science
• Bush doctrine
• Bush administration doctrine of military preeminence
• Iraq crisis, 2003