December 05, 2004
Preventive War--Posner
The U.S. invasion of Iraq, the U.S. decision not to invade Afghanistan before the 9/11 attacks, and concern with the apparent efforts of Iran and North Korea to obtain nuclear weapons raise acutely the question when if ever a preemptive or preventive war is justified. If “preemptive war” is defined narrowly enough, it merges into defensive war, which is uncontroversial; if you know with certainty that you are about to be attacked, you are justified in trying to get in the first blow. Indeed, the essence of self-defense is striking the first blow against your assailant.
But what if the danger of attack is remote rather than imminent? Should imminence be an absolute condition of going to war, and preventive war thus be deemed always and everywhere wrong? Analytically, the answer is no. A rational decision to go to war should be based on a comparison of the costs and benefits (in the largest sense of these terms) to the nation. The benefits are the costs that the enemy’s attack, the attack that going to war now will thwart, will impose on the nation. The fact that the attack is not imminent is certaintly relevant to those costs. It is relevant in two respects. First, future costs may not have the same weight in our decisions as present costs. This is obvious when the costs are purely financial; if given a choice between $100 today and $100 in ten years, any rational person will take $100 now, if only because the money can be invested and through interest compounding grow to a much larger amount in ten years. But the appropriateness of thus discounting future costs is less clear when the issue is averting future costs that are largely nonpecuniary and have national or global impact.
Second, and more important, and well illustrated by the failure to find weapons of mass destruction in Iraq, if the threat of attack lies in the future it is difficult to gauge either its actual likelihood or its probable magnitude. But this is not a compelling argument against preventive war. What is true is that a defensive war is by definition waged only when the probability of an attack has become one; the attack has occurred. The probability of attack is always less than one if the putative victim wages a preventive war, because the attacker might have changed his mind before attacking.
But while the probability of a future attack is always less than one, the expected cost of the future attack—the cost that the attack will impose multiplied by the probability of the attack—may be very high, perhaps because the adversary is growing stronger and so will be able to deliver a heavier blow in the future than he could do today. It may be possible to neutralize his greater strength, but that will require a greater investment in defense. Suppose there is a probability of .5 that the adversary will attack at some future time, when he has completed a military build up, that the attack will, if resisted with only the victim’s current strength, inflict a cost on the victim of 100, so that the expected cost of the attack is 50 (100 x .5), but that the expected cost can be reduced to 20 if the victim incurs additional defense costs of 15. Suppose further that at an additional cost of only 5, the victim can by a preventive strike today eliminate all possibility of the future attack. Since 5 is less than 35 (the sum of injury and defensive costs if the future enemy attack is not prevented), the preventive war is cost-justified.
A historical example that illustrates this analysis is the Nazi reoccupation of the Rhineland area of Germany in 1936, an area that had been demilitarized by the Treaty of Versailles. Had France and Great Britain responded to this treaty violation by invading Germany, in all likelihood Hitler would have been overthrown and World War II averted. (It is unlikely that Japan would have attacked the United States and Great Britain in 1941 had it not thought that Germany would be victorious.) The benefits of preventive war would in that instance have greatly exceeded the costs.
Posted by posner at 09:22 PM to | Comments (3) | TrackBack (0)
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Comments
Interesting comparison to invading germany after Hitler took the Rhineland as a justification to preemptive war.
Using that logic if Canada and Mexico were to attack America in a preemptive war because Bush invaded Iraq without cause and that they believed America was on a path to world domination - would that be justified?
Posted by: private at December 5, 2004 09:50 PM
A nitpick. The first word of the title is either mispelled or misused.
The content is high class and thought provoking. Thanks.
Posted by: Jim at December 5, 2004 10:03 PM
Society constructs certain rules, the widespread compliance with which allows for a reduction in various costs. The rule of honesty, for instance, might decrease contracting and contract enforcement costs; the rule against unprovoked violence allows people to invest less in personal protection and thus reduces the costs of transacting day-to-day business that involves walking on the streets.
The rule against attacking a nation unless attacked introduces a degree of certainty into international interactions that presumably allows everyone to reduce the cost of self defense. Once this implicit international consensus prohibiting preemptive war is broken, the costs of defense for all nations will likely rise. It is the discounted value of these future defense expenditures that Judge Posner appears to omit from his cost-benefit example. It seems that at least a plausible case can be made that this will not be a negligible term in the cost-benefit balance that might make the threshold at which preemptive action is justified (at least the first time) extraordinarily high.
Posted by: Paul Eremenko at December 5, 2004 10:12 PM
