Vice President Mike Pence looks toward the north from an observation post inside the demilitarized zone separating the two Koreas, in Paju, South Korea.Kim Hong-Ji / Reuters

A hidden assumption underlies the debate over North Korea. The assumption is that preventive war—war against a country that poses no imminent threat but could pose a threat in the future—is morally legitimate. To be sure, many politicians oppose an attack on practical grounds: They say the costs would be too high. But barely anyone in the foreign policy mainstream calls the idea itself abhorrent.

By historical standards, that’s astounding. Over the past two decades, American foreign policy has undergone a conceptual shift so complete that its current practitioners don’t even acknowledge how revolutionary their current views are. During the Cold War, the dominant figures in American foreign policy considered preventive war to be fundamentally un-American. A member of the Truman, Eisenhower, Kennedy, or Reagan administration, transported to 2017, would wonder how their successors embraced a principle that they associated with the regimes America fought in World War II.

In the second half of the 20th century, when America’s leaders heard “preventive war,” they thought about Nazi Germany and Imperial Japan. And for good reason. Both regimes had used the doctrine to justify their attacks in World War II. In August 1939, on the eve of his invasion of Poland, Hitler told his generals that, “we are faced with the hard alternative of either striking or the certainty of being destroyed sooner or later.” In a 2006 journal article, University of Pittsburgh law professor Jules Lobel quoted the Commander of the Japanese fleet, Admiral Yamamoto, as writing that, “[i]n the event of outbreak of war with the United States, there would be little prospect of our operations succeeding unless, at the very outset, we can deal a crushing blow to the main force of the American fleet in Hawaiian waters.”

Americans wanted a postwar system that outlawed such logic. In 1945, at the San Francisco Conference that founded the United Nations, the American delegate Harold Stassen explained that the United States “did not want exercised the right of self-defense before an armed attack had occurred.” Four years later, in August 1949, the Soviet Union tested an atomic bomb, ending America’s nuclear monopoly. Some in the military entertained the notion of destroying the USSR’s embryonic arsenal. But NSC 68, which in April 1950 famously outlined America’s strategy for fighting the Cold War, declared the notion unthinkable. “It goes without saying that the idea of ‘preventive’ war—in the sense of a military attack not provoked by a military attack upon us or our allies—is generally unacceptable to Americans,” it insisted. Four months later, when General Orville Anderson, commandant of the Air War College, suggested a preventive attack on the U.S.S.R., Harry Truman fired him. “We do not believe in aggressive or preventive war,” Truman told the nation. “Such war is the weapon of dictators, not of free democratic countries like the United States.”

Dwight Eisenhower agreed. The National Security Strategy his administration unveiled in 1955 declared, “[t]he United States and its allies must reject the concept of preventive war.” Secretary of State John Foster Dulles added that, “All of us have heard this term ‘preventive war’ since the earliest days of Hitler. … I wouldn’t even listen to anyone seriously that came in and talked about such a thing.”

During the Cuban Missile Crisis, John F. Kennedy listened. But he too rejected preventive war—not only because of the practical dangers of bombing the Soviet missiles being assembled 100 miles from Florida, but because of the moral stigma. “My brother,” declared Robert Kennedy, whose voice proved critical, “is not going to be the Tojo of the 1960s.”

Kennedy and Lyndon Johnson also let China go nuclear. In a 1957 speech, Mao had boasted that, “I’m not afraid of nuclear war. There are 2.7 billion people in the world; it doesn’t matter if some are killed. China has a population of 600 million; even if half of them are killed, there are still 300 million people left.” Nonetheless, Kennedy and Johnson watched as China moved towards its first nuclear test in October 1964.

As West Point Professor Scott Silverstone notes in his excellent book, Preventive War and American Democracy, the taboo against preventive war continued during the Reagan administration. When Israel bombed Iraq’s Osirak nuclear reactor in 1981, United Nations Ambassador Jeane Kirkpatrick declared the attack “shocking,” and worked with Iraq to craft a resolution condemning it and demanding “appropriate redress.” As punishment, the Pentagon delayed sending Israel a shipment of F-16 aircraft.

The shift began after the Cold War. The generation of policymakers with first hand memories of World War II was passing from the scene. The 1991 Gulf War had boosted confidence in the American military. And the adversaries seeking nuclear weapons were no longer great powers like the Soviet Union and China but smaller “rogue states” like Iraq, Iran, Libya, and North Korea, with less capacity to retaliate against an American attack.

In 1993, when North Korea threatened to withdraw from the Nuclear Non-Proliferation Treaty after it was caught secretly manufacturing plutonium, Secretary of Defense William Perry urged a preventive attack. When the commander of U.S. forces in Korea outlined the catastrophic war that might result, Bill Clinton rejected Perry’s advice. But, Silverstone notes, he did so on purely pragmatic grounds. In the administration’s internal deliberations, no one argued against preventive war on moral grounds. Conceptually, something had changed.

If Clinton peeked under a door that his predecessors had tried to bolt shut, George W. Bush flung it open. “Given the goals of rogue states and terrorists,” his administration declared in its first National Security Strategy after 9/11, “the United States can no longer solely rely on a reactive posture as we have in the past. The inability to deter a potential attacker, the immediacy of today’s threats, and the magnitude of potential harm that could be caused by our adversaries’ choice of weapons, do not permit that option. We cannot let our enemies strike first.”

This was mostly nonsense. Al-Qaeda, which had no regime to protect, may have been difficult to deter. But the Bush administration provided no evidence that deterrence would prove any less successful against “rogue states” like Iraq, Iran or North Korea than it had proved against Stalin and Mao. The National Security Strategy slandered Bush’s Cold War predecessors as “reactive.” Unable to grasp their principles, Bush mistook them for passivity.

Among the duplicities that attended Bush’s new doctrine was a linguistic one. Instead of admitting that he was embracing preventive war, Bush called it “preemption.” That was a lie. Preemptive war has an entirely different status in international law because it refers to an entirely different thing: a response to imminent attack.

The Iraq War should have discredited Bush’s frightening new doctrine. But the peculiar circumstances of the Iraq fiasco kept it alive. Because Saddam Hussein turned out not to be developing a nuclear bomb, rejecting the war didn’t require rejecting the doctrine that underlay it. The fact that Bush got the intelligence wrong obscured the fact that Iraq would have constituted a reckless departure from American tradition even if he had gotten the intelligence right.

Barack Obama illustrates the point. He won the presidency in part by opposing the war in Iraq. Yet he adopted one of its underlying assumptions when it came to Iran. Obama yearned to stop Tehran’s nuclear program diplomatically. But from the beginning of his presidency, he was clear: If diplomacy failed, his Plan B was not deterrence. It was preventive war.

Now Donald Trump is perpetuating that assumption when it comes to North Korea. Referring to the potential for Pyongyang to test an intercontinental ballistic missile that could carry a nuclear warhead, he tweeted, “It won’t happen.” This week Mike Pence declared that, “When the president says all options are on the table, all options are on the table. We’re trying to make it very clear to people in this part of the world that we are going to achieve the end of a denuclearization of the Korean peninsula—one way or the other.”

To legitimize preventive war, Trump’s advisors are resuscitating all the bad arguments made about Iraq and Iran. Kim Jong Un’s ballistic missile tests, argues UN Ambassador Nikki Haley, prove that he is “not a rational person.” Really? Kim is a monster. But from the standpoint of regime preservation, his pursuit of nuclear weapons is highly rational. Since 9/11, the United States has deposed governments in Iraq, Afghanistan and Libya. It just bombed regime targets in Syria. What do these regimes have in common? They couldn’t deter an American attack because they didn’t have nuclear weapons. The North Koreans refer over and over to Muammar Qaddafi, who abandoned his nuclear program in a bid to win the West’s affection, and ended up being sodomized by Libyan rebels who were using NATO as their air force. As Dartmouth’s David Kang has explained, “To dismiss North Korea’s security fears is to miss the root cause of North Korea’s actions.”

Hawks assert that Pyongyang cannot be deterred. But it has been deterred. North Korea first tested a nuclear weapon 11 years ago. It has possessed biological and chemical weapons since the 1970s or 1980s. Yet North Korea’s leaders have not used them, most likely because they know that doing so would imperil what they value most: their hold on power.

Nonetheless, media outlets, including The New York Times, abet Trump by calling his potential strike “preemption,” thus implying that the mere fact of a North Korean nuclear missile—or the mere fact that Pyongyang has threatened that if the U.S. were about to attack, it would so first (which actually would be “preemption”)—places the U.S. and its allies in imminent danger. Bush’s linguistic lie has triumphed. Preventive war has gained moral respectability even as it has disappeared from America’s lexicon.

It’s hard to recapture the horror that earlier generations of Americans felt about preventive war when it was still something that other countries did to the United States and not merely something Americans contemplate doing to others. They viewed it the way some Americans still view torture: as liberation from the moral restraints that human beings require. One of the things that frightened them most about the Nazis was that Hitler had dispensed with the concept of original sin. He had aimed to create a new class of infallible, god-like, humans who need not be encumbered by the fetters that bound lesser races. Totalitarianism, argued Arthur Schlesinger in The Vital Center, aimed “to liquidate the tragic insights which gave man a sense of its limitations.” For Schlesinger, Reinhold Niebuhr, Walter Lippmann and other intellectuals who shaped America’s foreign policy debate in the early Cold War, acknowledging these limitations was part of what made America different. Because Americans recognized that they were fallible, fallen creatures, they did not grant themselves the illegitimate, corrupting power of preventive war.

That humility has been lost. If asked whether China, Russia, or even France, has the right to launch wars against countries merely because those countries are building weapons that could one day pose a threat, Americans would quickly say no. They would recognize immediately that such a right, if universalized, threatens the peace of the world. Yet in both parties, policymakers grant that right to America. They do so even after Iraq. And even with Donald Trump in the White House.

It is now Americans who consider themselves a higher breed, capable of wielding powers that they would consider illegitimate and terrifying in anyone else’s hands. Are today’s leaders so much wiser and more moral than Truman, Eisenhower, Kennedy, and Reagan that they can be trusted with a power that made those men shudder? Let’s hope Americans never find out.

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