To contemplate the moral possibilities of the new world order at mid-century required a major mental adjustment. Power is never unlimited, wrote Alexis de Tocqueville more than a hundred years earlier. “Above it in the moral world,” he claimed, “are humanity, justice, and reason.” This had been a matter of long-standing faith in Western civilization. In the nineteenth century, much of Western society shared a strong moral consensus that permitted people to take for granted that moral scruples among “civilized” people invariably limited potential human barbarism. Some decades after Tocqueville, the American philosopher William James wrote that to argue that human beings enjoy free will is not to say “that everything that is physically conceivable is also morally possible. It merely says that of alternatives that really tempt our will more than one is really possible”; whereas, James argued, “Of course, the alternatives that do thus tempt our will are vastly fewer than the physical possibilities we can coldly fancy.”

For the witnesses of the Second World War and for their descendants, “vastly fewer” no longer appeared to apply. No horror, no cruelty seemed beyond human temptation. No quantity of civilian casualties, no number of innocent children or of aged, disabled, or helpless human beings, and no measure of human sympathy posed a limit on the indiscriminate death perpetrated in the course of the war. America's enemies – and, what was more chilling, Americans themselves – had shown both the technological and moral capacity for producing such devastation.

Americans' moral capacity for the indiscriminate murder of innocents would, in the next quarter-century, grow to horrific dimensions.