Early in the Cold War weapons of mass destruction met this requirement. They were prohibitively expensive, and only the richest two superpowers had nukes. But as the race progressed, warheads got cheaper. The cost of conventional weapons—submarines, fighters, and carriers, for example—soared, but the nuclear warheads themselves got smaller and cheaper. Pretty soon, England and France were testing nuclear warheads, then China and South Africa. By the 1970s India had successfully tested nuclear warheads, too, and by the 1990s so had Pakistan. Now, Israel and North Korea have them as well. The most important precondition for deterrence is disappearing.

Emlen, Douglas J, Animal Weapons_ The Evoluti…, loc. 602