In this essay, first published in the journal International Relations in 1986, Gaddis attempts to account for the fact that the period after the Second World War, which featured one of the "most bitter and persistent antagonisms short of war in modern history," did not result in a Third World War. This was despite the fact that war between the United States and the Soviet Union seemed very likely at several points throughout this period.
Gaddis finds the answer in the international system that developed after the war. While he does not ignore the bloodshed in places like Vietnam and Afghanistan (the Soviet Union was fighting there when Gaddis published the essay) he points to the relative stability of that system as its most salient feature. To explain this stability, Gaddis points to the "bipolarity" of the postwar arrangement, which was at once very dangerous and inherently more stable than the periods before the First and Second World Wars. The bipolar arrangement was simple, it did not require a skilled statesman to maintain it, and its alliance systems (like NATO and the Warsaw Pact) were strong enough that the actions of outsider states in Latin America and Asia in particular did not destabilize them.
Another thing that made it possible was that the two "bipolar" powers were independent of each other. They did not compete for trade, in particular, and they carved out two spheres of influence that only really overlapped in a few areas. Another major feature in promoting stability in this bipolar world was the possession, by both sides, of a nuclear deterrent.
"Consider," Gaddis observes, "what the effect of this mechanism would be on a statesman from either superpower who was contemplating war." The fact that both sides knew (after Hiroshima and Nagasaki) what these weapons could do to people, and that both sides had the ability to destroy the other naturally put a brake on the kinds of aggression that had contributed to wars in the past.
The doctrine of "mutually assured destruction" also encouraged both sides to use their influence to rein in third party states whose behavior was likely to lead to full-scale war. Both sides agreed (having really no choice) that nuclear weapons were only to be used as a last resort.
All of these factors, among others, Gaddis concludes, made the "bipolar" arrangement after the Second World War more stable, if not necessarily more conducive to human rights and social justice, than previous situations that led to war.