Seventy years ago first Hiroshima, then Nagasaki, were obliterated. Three generations later the grand-strategic consequences of those events can be discerned with reasonable clarity. They are by no means uniformly bad.
The claim that the destruction of two large cities and the killing of over two hundred thousand humans was justified in order to prevent an even greater carnage on both sides, resulting from the putative U.S. invasion of Japan in late 1945, is historically disputable and morally unsustainable. The horror itself—including the unexpected effects of radiation and fallout—has had a salutary impact on the great and minor powers alike in the ensuing decades, however. It is arguable that its deterrent effect has spared the world a major war costing millions of lives.
In most bipolar confrontations known to history—from Assyria versus Egypt, Persia vs. Greece, Athens vs. Sparta, and Rome vs. Carthage onwards—coexistence (peaceful or otherwise) was not an option. In a classic bipolar model, America and the USSR likely would have gone to an all-out war some time 10-15 years after 1945, a war probably no less destructive than the one preceding it. The constraints against first use of nuclear weapons, and the related fear of escalation leading to their inadvertent application, introduced an element of caution and moderation on both sides—the “nuclear taboo.” A complex system of informal checks and balances within the political, military and bureaucratic apparata operated in different ways on different sides of the Iron Curtain, but its effects were broadly similar. It was in evidence in the U.S. for the first time in the critical Korean winter of 1950-51, when President Harry Truman overruled General Douglas MacArthur. President Eisenhower did say in 1955 that nuclear weapons could be used “just exactly as you would use a bullet or anything else,” but during the 1958 Taiwan Strait Crisis he admitted that, with the bomb, “you cross a completely different line.” That line was in Central Europe and in the homeland then, and it had remained there until the fall of the Wall. Restraint was notably present on both sides during the Cuban Missile Crisis of 1962: ideological differences and divergent strategic interests were transcended by mutually compatible rational calculations. Neither side seriously considered the possibility of preemptive attacks thereafter, Nixon’s and Kissinger’s fleeting “madman” threats to Hanoi notwithstanding.