- See also: Preemptive attack
Preventive attack is a military doctrine in which an actor uses military force on an opponent that it considers as presenting a long-term threat. Such an opponent is not believed to be about to start offensive warfare; a spoiling attack to disrupt the preparations for offensive warfare is preemptive attack. Preemptive attack implies a response to an immediate danger. It is clearly not an act of immediate self-defense as defined by Article 51 of the United Nations Charter. the National Security Strategy of the United States, as stated by the George W. Bush Administration, does consider preventive war as one of many grand strategic options against terrorism and weapons of mass destruction. 
A good deal of European opinion, however, does not consider preventive war to be justified. Many historians, of course, speculate about the what-ifs had there been preventive action against Hitler moving into the Sudetenland or Czechoslovakia, which clearly were not immediate threats against France and the United Kingdom. By Carl Bildt
Charles Western quotes Nye's definition that
A premptive war occurs when statesmen believe merely that war is better now than later A preemptive strike occurs when war is imminent. 
To qualify an act as preemptive, it must comply with three criteria, first established by Daniel Webster in the Caroline case of 1842. If these criteria do not apply, the action is, at best, preventive. The Caroline was a U.S. ship in Canadian waters, sunk by the Royal Navy because it was believed to be supporting rebels. The criteria, to give the act legitimacy are:
- imminence: There was an immediate and plausible threat. Self-defense does not require taking the first blow.
- proportionality: the amount of force must be appropriate to neutralize the threat, but not more.
- necessity or "window of opportunity": There will be no later opportunity to spoil the enemy attack. While this was fairly straightforward in cases involving massed combat aircraft on airfields, it is much more difficult with respect to non-national terrorists, because the only opportunity to attack them may be while they are known to be in a base area, rather than secretly approaching the target.
The term suggests that the opponent has hostile intentions to the actor; simply attacking to seize land or resources is rarely considered prevention by objective observers, although propagandists may describe it as such. Japanese invasions of multiple locations in Asia, in 1941, were not seriously called preventive, but justified in that Japan needed the resources in the Dutch East Indies, Indonesia, etc., for its own development.
The Japanese could make more of a case that the Battle of Pearl Harbor was preventive, but certainly not preemptive. From their standpoint, it was necessary to their long-term success that the United States Pacific Fleet be neutralized. In contrast, the Nazi staged attacks at their own Gleiwitz radio station, which were a pretext for a punitive attack on Poland, cannot be reasonably justified as preventive, as the Polish military was not a plausible threat against Germany even in the future.
While prevention is usually assumed to start from a condition of relevant peace, the term has been used to describe attacks against major capabilities of an overt opponent, such as the British attacks, in August 1943, against the German long-range guided missile development center at Peenemunde. This, of course, was within the context of an ongoing war, and indeed a larger operational plan against missile threat, Operation CROSSBOW.
Another example was the British offer to the French fleet, at Mers-al-Kebir in July 1940, after the surrender of France to the German. The officer commanding Operation CATAPULT was under orders to prevent the French ships from being used against Great Britain. He gave a number of options short of combatm including joining his fleet, going to a neutral port to be interned, and sinking (i.e., scuttling) themselves. When all more peaceful options refused, the British unit opened fire on the French ships. 
In the contemporary context, the term has been applied to narrowly focused attacks against presumed weapons of mass destruction facilities, such as the 1981 Israeli attack on the Iraqi nuclear reactor, under construction at Osirak. While WMD capability was one of the targets for the 2003 Iraq War, there were other factors such as generic regime change and support of terrorism. Some analysts do accept calling that attack preventive, while others do not.
- Grimmett, Richard F. (2003), U.S. Use of Preemptive Military Force, Congressional Research Service, Library of Congress, CRS report for Congress, RS21311
- , Chapter VII: Action with Respect to Threat to the Peace, Breaches of the Peace, and Acts of Aggression, Article 51, United Nations Charter, United Nations
- George W. Bush (2006), III. Strengthen Alliances to Defeat Global Terrorism and Work to Prevent Attacks Against Us and Our Friends. C: The Way Ahead, National Security Strategy of the United States
- Reiter, Dan (April 2006), Preventive War and its Alternatives: the Lessons of History, Strategic Studies Institute, U.S. Army War College, pp. 2-11
- Bildt, Carl (13 January 2003), Pre-emptive military action and the legitimacy of the use of force: Remarks from a European perspective, CEPS/IISS European Security Forum, Brussels, 13 January 2003
- Western, Charles A. (June 17, 2005), Abroad, in Search of Monsters to Destroy: The United States and the Future of Preemption, U.S. Army Command and General Staff College, pp. 9-10
- Nye, Joseph S. (2003), Understanding international conflicts: An introduction to theory and history, Longman, p. 157
- Western, pp. 44-46
- "Peenemunde - 1943", Globalsecurity
- Johnson, Max, Operation CATAPULT - Mers-el-Kebir - 3RD JUL 1940
- "Osiraq / Tammuz I", Federation of American Scientists