In one of the most quoted aphorisms in international relations, the Prussian political philosopher Carl von Clausewitz said that "war is merely a continuation of politics." In other words, for every war that has been waged, we can point to political aims underpinning its waging. Take some recent examples. In large part, the 1991 Persian Gulf war was about exerting power: It sought to prevent an invasion of Saudi Arabia and oust Iraqi forces from Kuwait. However, in Vietnam, the end goal was political influence: The war was fought to keep the south from falling to the communists. The examples are just two among many, but interestingly, they are illustrative of when war works, and when it doesn't.
Indisputable is the fact that war is the most powerful weapon in the foreign policy arsenal, but looking closer it's clear that war may also be the most limited. According to a new investigation by two political scientists, since World War II, the major powers -- Russia, France, China, England, and the U.S. -- have launched 126 foreign military interventions. Viewed together, it's clear that to project power, yes, war works. But to pursue political ends (an entirely different goal), war is a largely deficient means. Consequently, the engineers of American foreign policy would be wise to consider that exerting influence within an international order that more and more turns on political interventions and less and less on state-based conflict means less conquering the enemy with warfare and more engagement by innovative and constructive means.
First, power and politics have to be understood as being separate and distinct. The new study in the Journal of Peace Research by Patricia Sullivan and Michael Koch measured the outcomes of 126 wars waged by the great powers since World War II against the original political aims for which they were launched. In terms of the gross extension of power -- overthrowing a foreign government or defending an ally from an impending threat, for instance -- war worked almost all the time. (Think 1991 Persian Gulf.) However, when the end goal was imposing politics, not even a third of the missions were successful. (Think Vietnam.) According to Sullivan and Koch, "Major power states are least likely to be successful when they attempt to coerce a foreign government into changing its foreign or domestic policy."