In the domestic debate about the nuclear agreement between Iran and the P5+1 nations including the United States, it is often routinely asserted, by Democrats and Republicans alike, that “all options are on the table,” including “the military option,” by which is meant an unprovoked preventive war by the United States or perhaps Israel to destroy Iranian facilities which might be used to produce nuclear weapons. The casual and widespread acceptance of “the military option” is a disturbing development.

Before the presidency of George W. Bush, preventive war was not considered a legitimate tool of anti-proliferation by the United States. In 2003, the United States fought the only preventive war in its history, on the pretext of preventing Saddam Hussein from obtaining weapons of mass destruction. The inadvertent result was the disintegration of Iraq, a regional Sunni-Shia proxy war and the emergence of the Islamic State. The preventive war against Iraq was the stupidest blunder in the history of U.S. foreign policy. That some Americans today, only twelve years later, can even consider the possibility of repeating that blunder in the case of Iran is as remarkable as it is appalling.

International law distinguishes between preemptive war, which is legal, and preventive war, which is not. In 1842, following an incursion into U.S. territory by British forces against anti-British Canadian rebels, Secretary of State Daniel Webster made the classic observation that a preemptive attack is justified only when a state can “show a necessity of self‐defence, instant, overwhelming, leaving no choice of means, and no moment for deliberation.”

Six years later, in 1848, Abraham Lincoln dismissed the Polk administration’s use of Texas-Mexico border skirmishes as an excuse for the invasion, occupation and dismemberment of Mexico: “If, today, [the president] should choose to say he thinks it necessary to invade Canada to prevent the British from invading us, how could you stop him? You may say to him, 'I see no probability of the British invading us'; but he will say to you, 'Be silent; I see it, if you don't.’”

The distinction between preemptive and preventive war is a matter of common sense and basic morality. In December 1941, the United States would have been justified in defending itself by attacking the Japanese fleet before it could reach Pearl Harbor. But it would have been criminal folly if the United States had bombed Japanese factories and shipyards in 1921, on the theory that some of their output might be used in a sneak attack on the United States at some point in the next few decades.

Incurring the costs of war to avert a speculative future threat which may never materialize is the antithesis of realpolitik. Otto von Bismarck, one of history’s great realists, is often quoted as saying “preventive war is like committing suicide for fear of death.” In his memoirs, Bismarck considered “the question whether it was desirable, as regards a war which we should probably have to face sooner or later, to bring it on anticipation before the adversary could improve his preparations.” Bismarck argued that the uncertainties were too great—“one cannot see the cards of Providence far enough ahead.”

Following the unprovoked June 7, 1981 Israeli air strike against Iraqi nuclear facilities in Osirak, Iraq, the Reagan administration supported a unanimous UN Security Council resolution which condemned the Israeli raid. Reagan’s ambassador to the United Nations, Jeane Kirkpatrick compared the “shocking” Israeli attack to the Soviet invasion of Afghanistan. British Prime Minister Margaret Thatcher, like Reagan a conservative friendly toward Israel, also condemned the raid. Thatcher told the House of Commons: “Just because a country is trying to manufacture energy from nuclear sources, it must not be believed that she is doing something totally wrong.”

The repudiation of preventive war as a tool of statecraft has served the United States and its allies well. Unfortunately, to justify its unnecessary and disastrous invasion of Iraq in 2003, the administration of George W. Bush sought to redefine preemptive war so broadly that the distinction between preemptive and preventive war collapsed. Bush’s strategy was encapsulated in the 2002 National Security Strategy:

"For centuries, international law recognized that nations need not suffer an attack before they can lawfully take action to defend themselves against forces that present an imminent danger of attack. Legal scholars and international jurists often conditioned the legitimacy of preemption on the existence of an imminent threat—most often a visible mobilization of armies, navies, and air forces preparing to attack.

We must adapt the concept of imminent threat to the capabilities and objectives of today’s adversaries. Rogue states and terrorists do not seek to attack us using conventional means.

The United States has long maintained the option of preemptive actions to counter a sufficient threat to our national security. The greater the threat, the greater is the risk of inaction—and the more compelling the case for taking anticipatory action to defend ourselves, even if uncertainty remains as to the time and place of the enemy’s attack. To forestall or prevent such hostile acts by our adversaries, the United States will, if necessary, act preemptively.

The United States will not use force in all cases to preempt emerging threats, nor should nations use preemption as a pretext for aggression. Yet in an age where the enemies of civilization openly and actively seek the world’s most destructive technologies, the United States cannot remain idle while dangers gathers."

John Yoo was one of the principal authors of the Bush administration’s infamous and now repudiated “Torture Memos,” claiming that it was legal for the president to order waterboarding, sleep deprivation, stress positions and other forms of physical and mental torture. Now a law professor at Berkeley, Yoo has set forth perhaps the most extreme defense of preventive war in a co-authored essay in 2009 for the Harvard Journal of Law and Public Policy entitled “The ‘Bush Doctrine’: Can Preventive War Be Justified?” The essay seeks to erase the distinctions between preemptive war, preventive war, and preventive strategy.

Much if not most strategy, by the United States and any country, is preventive, in the sense that its goal is to forestall dangerous situations in the future. The United States intervened in both world wars, once they had begun, rather than wait and risk confronting a victorious Germany later. America’s Cold War alliance against the Soviet Union was another preventive strategy.

But containment was an alternative to the crackpot idea of unprovoked preventive war against the Soviet Union, rejected by Presidents Truman and Eisenhower and every subsequent president during the Cold War. To treat both preventive balance-of-power strategies and unprovoked preventive wars as equally legal and equally legitimate examples of “pre-emption,” broadly defined, is as sophistical as saying that waterboarding is not torture.

The debate is not purely theoretical, as the preventive strikes and wars against Iraq by both Israel and the United States demonstrate. Ironically, the long-term failure of the Israeli raid in 1981 to eliminate Saddam’s weapons programs was taken for granted by the neoconservatives. They justified the Iraq War of 2003 as a preventive war, a kind of second Osirak raid on a colossal scale, which would eliminate the still-existing threat of Iraqi weapons of mass destruction—weapons which, following the invasion and occupation, turned out to be nonexistent.

What about dangerous regimes which, unlike Iraq, really have developed nuclear weapons or other WMDs? The United States did not go to war with Stalin’s Soviet Union, Mao’s China, or North Korea to prevent those militant totalitarian states from obtaining nuclear weapons.

China obtained its first nuclear weapons at the height of Mao’s militancy during the Cultural Revolution, following the catastrophic Great Leap Forward. At the time, the United States was engaged in a bloody proxy war with China in Vietnam, having already fought China directly a decade earlier in Korea. Should the Kennedy or Johnson administrations have bombed or invaded China to prevent Mao’s then-radical regime from acquiring nuclear weapons? The examples of the Soviet Union, China and North Korea suggest that if Iran develops nuclear weapons in the future it, too, can be deterred from using them by other states, including the United States and also Israel, which is widely believed to be the only state in the Middle East with its own nuclear arsenal.

Then there are the practical consequences of the so-called “military option” of disarmament by means of bombing or other methods of preventive war. How can blasting laboratories into rubble be a rational way to get rid of the dangerous substances they contain? What if nuclear materials are looted from the wreckage? What if bombing a facility with biological weapons unleashes a pandemic? For questions like these, the American policymakers and pundits who talk tough in public about “the military option” and “keeping all options on the table” have no plausible answers.

Like torture and genocide, preventive war is a foreign policy option which civilized countries deny to themselves, at some cost if necessary. Individual countries and the international community have many legal and legitimate options for preventing countries from obtaining weapons of mass destruction, but preventive war is not and should not be one of them. Margaret Thatcher was right in 1981: “Armed attack in such circumstances cannot be justified.”