Deterrence makes someone not do something. A parent promotes good teen behavior not just by providing cars and smartphones, but also by the explicit specter of graduated punishments that an adolescent does not wish to repeat, and thus chooses instead to abide by the house rules.
In terms of world affairs, a clear display of overwhelming military strength, and the real probability of being willing to use it, remind would-be aggressors not to start stupid conflicts — given that the possibility of winning something through war is overshadowed by the risk of losing far more. A world where everyone knows the unspoken rules as well as the moral and material relative strength and weakness of the various nations is a safer place for all involved.
Or put another way, deterrence, in the famous formulation of the 17th-century British statesman George Savile, 1st Marquess of Halifax, means that “Men are not hanged for stealing horses, but that horses may not be stolen.” Translated, that means that nations do not go to war just over Czechoslovakia, but that other nations are not swallowed up like Czechoslovakia.
When German foreign secretary Arthur Zimmermann, in a notorious 1917 telegram, offered the government of Mexico all sorts of rewards for attacking the southwestern United States and thereby sidetracking American support for the allies on the Western Front, Mexico balked. But its reason for backing off was not that it liked Americans or thought a preemptive attack would be unfair. Rather, President Carranza worried that Mexico lacked the military clout to take American territory. And even if it could have grabbed, say, Texas, Mexico did not have the power to control it — given a rowdy and armed English-speaking state population, one that Carranza worried was “better supplied with arms than most populations.” In other words, the Second Amendment and a frontier attitude helped to deter Mexico from taking up Zimmermann’s offer.
