Preemptive war, (begun by a "preemptive strike"), is defined by Michael Walzer in his book, Just and Unjust Wars as an attack initiated in response to a serious, imminent, and mounting risk to the two basic rights that sovereign states have, these being:
  1. Territorial integrity, or, the right not to be annexed or invaded by foreign forces; and


  2. Political sovereignty, or, the right to assert legal, paramilitary, and military control within the boundaries of the state's own territory.

The example Walzer offers is that of the Six Day War between Israel and Egypt (and Syria and Jordan too), in which Israel attacked first. Walzer argues that even though Israel attacked first, their action was a "preemptive" attack, which is always justified. It was preemptive because Egyptian forces were preparing to attack Israel within a few days, and other Arab countries had placed their armies under the command of Egyptian military commanders. When Israeli intelligence confirmed this, they dispatched their air forces into Egyptian airspace, and attacked Egyptian air bases and planes on the ground. This effectively rendered the Egyptians impotent.

In preemptive war, the attacker is thwarting an attack that would be happening "imminently," presumably in a matter of days, and when the only other alternative is to sit and wait to be attacked.

"Preventive" war, on the other hand, is an attempt to prevent a state from becoming sufficiently powerful to launch an attack. Preventive war is an unjustifiable response to a much more distant threat -- a threat that may not even exist at all. The difference is crucial, and the two terms, "preventive" and "preemptive", have unfortunately similar meanings in everyday parlance. There are many examples of preventive wars that have been popularly mis-labeled as "preemptive." The reasons for this misuse are sometimes measured and sinister, and at other times, the reason is mere stupidity and/or ignorance.

It is important to distinguish preemptive attacks, wars, or strikes, from "preventive" attacks, or "preventive war", which, in Walzer's view, are acts of aggression, and never justified. An example of a preventive, (not preemptive) war is the (wonderfully euphemistic), "Operation Iraqi 'Freedom'."

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