The number of nuclear-armed states that have been downgraded to ordinary states is also exceedingly small. Three former Soviet republics—Belarus, Kazakhstan, and Ukraine—relinquished their nuclear arms and agreed to not produce new ones after the fall of the Soviet Union. But they inherited those weapons from the U.S.S.R. and never had full authority over them. Not only did the Russian military control the weapons, but the republics “didn’t have people who could assemble nuclear weapons, who could maintain nuclear weapons,” according to Perkovich. The three nations returned the nuclear weapons stationed on their soil to Russia, where the arms could be destroyed, in exchange for something they coveted more at the time: American diplomatic and economic support for the newly independent countries. The unraveling of the Soviet Union “happened so quickly that political parties didn’t mobilize in those countries and say, ‘Wait a minute. We can get a better price,’ or, ‘Wait a minute. Russia may become nasty again,’ etc.,” Perkovich said.

The sole precedent for the type of outcome the U.S. is seeking on the Korean Peninsula is South Africa, which secretly embarked on a nuclear-weapons program in the mid-1970s out of concern that the Soviet Union was expanding its influence in southern Africa. (The Soviet Union had, for example, supported African liberation movements and Cuba’s military intervention in Angola.) The fear was that the Soviets might turn to South Africa next. Since South Africa was increasingly isolated internationally as a result of apartheid, its system of racial segregation and discrimination, the country’s leaders weren’t sure they could count on assistance from the United States and its allies in the event of aggression by the Soviets or their local proxies. So they developed half a dozen “Hiroshima-type” atomic bombs as a “deterrent,” according to former South African President F.W. de Klerk.

It was de Klerk who made the decision to do away with a nuclear-weapons program that he controlled. I spoke with him to get a sense of what motivated him to make a move that no one else in history has.

The thinking behind South Africa’s nuclear program was “If we have nuclear weapons, and if we then would disclose in a crisis [involving the Soviet Union] that we have it”—by, for instance, informing Western powers of their nuclear capability or conducting a nuclear test and threatening to use the device—then the Americans might be persuaded to come to South Africa’s defense rather than risk nuclear war, de Klerk told me.

De Klerk cited three reasons why he took the step, after becoming president in 1989, to dismantle South Africa’s nuclear arsenal and sign the international nuclear nonproliferation treaty. To begin with, he himself was opposed to nuclear weapons. When he first learned of South Africa’s covert nuclear program, as energy minister in the early 1980s, he said that he “never felt comfortable with it” but “couldn’t stop it.” He felt that it would be “meaningless to use such a bomb in what was essentially a bush war—that it was unspeakable to think that we could destroy a city in one of our neighboring countries in any way whatsoever.” The nuclear program struck him as “a rope around our neck,” he added. “You have something which you never intend to use, really, which is unspeakable to use, which would be morally indefensible to use.”