This article is part of a series from the November 2017 Harvard University conference entitled “Presidential First Use: Is it legal? Is it constitutional? Is it just?” To access all of the transcripts from this conference, click here.

Is the first use of nuclear weapons just? Is it morally right? This question applies not only to presidential first use but to first use by any state or non-state actor. Here is an ancient motto that has recently taken on an ominous new meaning: Fiat iustitia, pereat mundus (“Let justice be done, though the world perish”). Sometimes this motto is phrased as Fiat iustitia, ruat caelum (“Let justice be done, though the heavens fall”). Both versions urge that you should do what is right no matter how horrendous the consequence might be.

In the 16th century the Holy Roman Emperor Ferdinand I chose that first motto and used it as his armies fought the invading forces of the Ottomans led by Suleiman the Magnificent. Ferocious as those battles were, however, Ferdinand could never have imagined that the world would in fact perish as a result of his fighting what he thought was a just war.

Since Hiroshima and Nagasaki, the metaphors of the world perishing or the heavens falling have taken on far more literal meanings. When we think about justice and war, three main views prevail. One is the so-called realist view that war is hell, that justice is not an issue in war and never has been. The second is the pacifist view that wars are never just. The third is Just War Theory, which argues that there can be morally acceptable wars if they are waged for justifiable purposes such as national self-defense, but only if going to war is the last resort, and if war never explicitly targets noncombatants or uses inhumane weapons. Nuclear war cannot meet any of the conditions for a just war, because it would obliterate the distinctions between self-defense and aggression, combatants and noncombatants, and more or less inhumane weapons.

Michael Walzer, in his book Just and Unjust Wars, put it this way: “Nuclear weapons explode the theory of just war.” Any use of nuclear weapons is unjust because it endangers vast numbers of civilians and employs the most inhumane of weapons. Any first use of such weapons is precisely not launched as a last resort. Can we say the same, however, about policies that merely warn of or threaten the resort to nuclear weapons?

Proponents of first use argue that there should be no moral constraints on what a nation can do or threaten in self-defense and that threatening to use nuclear weapons is quite different from actually doing so; in their view, such threats are a form of deterrence. Ordinary moral constraints should allow for limited exceptions as a last resort when self-defense is at issue. Invoking self-defense as justification for going to war rests on a longstanding analogy between nations defending themselves and individuals doing so by means of violence as a last resort if need be.

But we need look no further back than to the wars in Vietnam and Iraq to see misuses of that language of self-defense. Those misuses led the United States and other nations to violate the most basic moral constraints regarding engaging in war as a last resort and in a way that spares civilians and prohibits inhumane weapons.

Just as wagers of wars past once took for granted that God was on their side, so self-defense and national security are invoked today even for aggressive ventures far beyond national borders. Such actions are hardly analogous to what an individual might rightfully do as a last resort when faced with direct assault. Indeed, the ferocity of today’s weapons and the genuine threat those weapons pose to national survival now lead governments often to argue that every action they take to reinforce their own power or to diminish that of their enemies contributes to self-defense.

During the 1980s, when the world lived with a balance of terror, the North Atlantic Treaty Organization (NATO) insisted on retaining a policy of first use. The member nations argued that nuclear deterrence by itself might not suffice if Soviet conventional forces moved into Europe. NATO’s only way to guard against such a move would be to rely on the threat of first use of nuclear weapons. At the same time, there was growing unrest in Europe, caused by the fear that the great powers intended Europe to be the theater where they would clash. Peace movements were mobilizing, calls were made for more complete test bans, for nuclear-free zones, for the elimination of the use of cruel weapons and cruel methods of warfare, and for the rejection of first-use policies.

In 1982 McGeorge Bundy, George Kennan, Robert McNamara, and Gerard Smith published an influential article that urged that the time had come for NATO to reconsider the policy of first use. “We think a policy of no-first-use, especially if shared with the Soviet Union, would bring new hope to everyone in every country whose life is shadowed by the hideous possibility of a third great twentieth-century conflict in Europe—conventional or nuclear.” Thirty-five years later, the fear of a third great conflict to which they referred as a hideous possibility has returned.

Kofi Annan, secretary general of the United Nations from 1997 to 2005, recently recalled his feeling of great relief at the collapse of the Berlin Wall in 1989, the sudden sense that, “with the end of the Cold War, the UN could do what it was set up to do, without one country vetoing the other”; world leaders would realize that “cross-border cooperation was the only way to solve crises.” Yet now, Annan said, “we seem to be back to where we were in ’89.” He added that men in high places “don’t always seem to understand the risks we are all in,” and warned: “All that we need is one miscalculation … and all bets are off.”

That same sense of urgency and high risk was expressed by the Norwegian Nobel Committee when awarding the 2017 Nobel Peace Prize to the International Campaign to Abolish Nuclear Weapons (ICAN). The Nobel Committee’s citation explained that “we live in a world where the risk of nuclear weapons being used is greater than it has been for a long time.” The number of states with nuclear weapons has increased and so has the intense distrust among nuclear adversaries. There is greater risk than ever that nuclear weapons might be launched accidentally, in error, or utterly irrationally. Just as the popular movement in Europe contributed to public debate and to bringing about change during the 1980s, so ICAN is today joining with environmental and other kinds of groups to achieve a treaty-based prohibition of nuclear weapons.

By drawing attention to the catastrophic consequences for the peoples of the world of any use of nuclear weapons, these groups aim to raise awareness of what genuine concern for collective self-defense calls for on the part of the peoples around the world. This is a use of the language of self-defense that we need to support: the collective self-defense of all the people who might be the victims of horrendous nuclear catastrophe. As President Reagan and General Secretary Gorbachev jointly declared in 1985: “A nuclear war cannot be won and must never be fought.”