Preemptive warfare is the practice of attempting to avoid an enemy's seemingly imminent attack by taking military action against them first. It is undertaken in self-defense. Preemptive war is often confused with preventive war, which is an attack launched to defeat a potential opponent and is an act of aggression. Preemptive war is thought to be justified and honorable, while preventive war violates international law. In the real world, the distinction between the two is highly contested.

In First Strike, Matthew J. Flynn examines case studies of preemptive war throughout history, from Napoleonic France to the American Civil War, and from Hitler's Germany to the recent U.S. invasion of Iraq. Flynn takes an analytical look at the international use of military and political preemption throughout the last two hundred years of western history, to show how George W. Bush's recent use of this dubiously "honorable" way of making war is really just the latest of a long line of previously failed attempts.

Balanced and historically grounded, First Strike provides a comprehensive history of one of the most controversial military strategies in the history of international foreign policy.