Nuclear Weapons and the Just War Tradition

While critics of nuclear arms often describe them as indiscriminate weapons that would be used to target civilian population centers, U.S. nuclear planning is deliberately aligned with the moral values that govern the U.S. way of war.

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Critics of nuclear arms often describe them as indiscriminate weapons that would be used to target civilian population centers. This argument ignores the realities of U.S. nuclear weapons policy and planning. While nuclear weapons are magnitudes more destructive than even the most powerful conventional weapons, this does not immediately render them unusable under traditional Just War constraints. In fact, U.S. nuclear planning is deliberately aligned with the moral values that govern the U.S. way of war. Proponents of nuclear disarmament ignore or minimize this point. Nonetheless, the implications are significant: by adhering to its moral principles while developing nuclear strategy, the United States enhances the credibility of its deterrent posture.

A Renewed Moral Debate

Nuclear weapons pose a moral paradox. Despite their role in preserving peace, the ability of nuclear weapons to wreak widespread destruction has raised concerns over their morality since the Cold War. Early weapon systems lacked accuracy and carried high-yield warheads, raising the prospect of civilian deaths on a large scale. Questions of whether such systems could be employed under the Just War tradition were vigorously debated, and various moral frameworks were applied to explain the apparent contradictions of deterrence. Utilitarianism, for example, emphasized the peace that nuclear deterrence enabled, therefore justifying threats against civilians. One of the most high-profile moral pronouncements on nuclear deterrence, the U.S. Catholic Bishops’ 1983 pastoral letter, gave grudging approval to nuclear deterrence but urged the world to quickly move beyond the status quo, noting that deterrence is “a transitional strategy justifiable only in conjunction with resolute determination to pursue arms control and disarmament.”

Today, the morality of nuclear weapons has reemerged as a major topic, thanks to dissatisfaction with the perceived slow pace of global nuclear disarmament, concerns about nuclear war on the Korean Peninsula, and international efforts to outlaw nuclear weapons. In October 2017, the Nobel Peace Prize went to the International Campaign to Abolish Nuclear Weapons (ICAN) in recognition of its promotion of the Treaty on the Prohibition of Nuclear Weapons (TPNW). To date, 58 nations have signed the TPNW, although none of them are nuclear-armed countries. Among other claims, the treaty asserts that any use of nuclear weapons would be “contrary to the rules of international law applicable in armed conflict.” Pope Francis has thrown his moral weight behind the treaty, stating that nuclear weapons have “devastating, indiscriminate and uncontainable effects, over time and space.” The head of ICAN, Beatrice Fihn, has said that if “the U.S. nuclear arsenal all went off, it could kill civilization.”

On the other side of the debate, the United States has consistently objected to the TPNW as unrealistic and dangerous to the existing nonproliferation regime. The nuclear debate has thus come into sharp relief between those who see a potential for catastrophe if nuclear weapons are used and countries unable to see a realistic way of moving beyond nuclear deterrence without sacrificing international stability.

Just War and Nuclear Weapons

Two approaches seek to resolve the paradox surrounding the morality of nuclear weapons. Advocates of nuclear disarmament, such as ICAN, work to delegitimize and ban nuclear weapons. In contrast, the United States strives to preserve their legitimacy by reserving nuclear weapons for extreme circumstances and even then applying the law of armed conflict when considering their possible use. As former United States Strategic Command (USSTRATCOM) commander General Robert Kehler recently noted, “the law of war governs the use of U.S. nuclear weapons. Nuclear options and orders are no different in this regard than any other weapon.”

The Just War tradition, which underpins the modern law of armed conflict, breaks the moral analysis of war into two segments: jus ad bellum considerations (when is recourse to war morally justified?) and jus in bello considerations (how can a war be fought in accordance with moral principles?). This article focuses on the criteria for prosecution of a nuclear war in accord with the jus in bello principles of discrimination and proportionality.

The principle of discrimination dictates that non-combatants may not be intentionally targeted during a war. Countries are obliged to conduct their war planning to minimize collateral damage to the extent feasible. The quantitatively higher capacity of nuclear weapons to inflict collateral damage makes critical analysis of nuclear targets even more important than those targets to be attacked by conventional arms. According to the most recent report to Congress on U.S. nuclear employment strategy, U.S. forces must retain “significant counterforce capabilities against potential adversaries.” U.S. strategy “does not rely on “counter-value [i.e. targeting population centers] or “minimum deterrence” strategy.”

Critically, the Just War tradition avoids imposing a standard that all civilian casualties must be avoided (something no country could achieve without the risk of losing an otherwise legitimate war). Instead, the tradition levies a more realistic standard that collateral damage must be avoided to the extent feasible while in pursuit of legitimate military objectives. Charles Dunlap, a former Staff Judge Advocate at USSTRATCOM, highlights the ability of nuclear weapons to be used discriminately, noting that “by reducing weapon yield, improving accuracy through delivery system selection, employing multiple small weapons (as opposed to a single, large device), adjusting the height of burst, and offsetting the desired ground zero, collateral damage can be minimized consistent with military objectives.”

The international community itself has not seen fit to judge all potential nuclear weapons use as disproportionate.

The jus in bello principle of proportionality obliges a nation to employ only the amount of force necessary to achieve its military objectives. Assuming that the principle of discrimination is satisfied, proportionality requires the damage likely to be created by an attack to be weighed against the legitimate military objectives to be achieved. This principle goes to the heart of nuclear weapons use, due to the potential destructive power of nuclear weapons and their lingering aftereffects. It is the United States’ sensitivity to the principle of proportionality that has led to a consistent position, included in its most recent Nuclear Posture Review, that the “United States would only consider the employment of nuclear weapons in extreme circumstances to defend the vital interests of the United States, its allies, and partners.” As Elbridge Colby has pointed out, “If the destruction of a target is critically important, it may be permitted under classical law-of-war doctrine if the ancillary damage is not intended and its costs do not outweigh the legitimate object achieved.” In addition, the international community itself has not seen fit to judge all potential nuclear weapons use as disproportionate. The International Court of Justice’s 1996 opinion on the lawfulness of nuclear weapons left open the possibility that nuclear weapons could be used lawfully in a case where the survival of the state was at risk.

As a result, a complete analysis of the moral aspects of nuclear weapons begins by separating the devastation nuclear weapons are capable of inflicting from the way in which the United States actually plans to employ them. It also recognizes the tradeoffs inherent in the prudential decisions over retaining nuclear weapons; specifically, whether steps toward nuclear disarmament could prove destabilizing or hold more risk than the continued nuclear deterrence relationships in place today. In addition, a moral analysis of U.S. nuclear planning needs to be grounded in the present historical moment, and acknowledge that U.S. nuclear strategy has changed significantly over time and has evolved to align with the country’s moral values.


Despite what disarmament advocates claim, nuclear war plans can be consistent with Just War criteria. The U.S. record in applying Just War principles to nuclear planning indicates it will act in a morally responsible way, even if it must consider using nuclear weapons. By doing so, the United States continues to apply decades of deterrence theory that suggests that threats must be credible in order to deter. Potential adversaries could be more willing to gamble that the United States would avoid using its own weapons in a conflict if doing so would create a stain on the United States’ national conscience. As Albert Wohlstetter put it in 1983, “Western nonsuicidal threats against legitimate military targets are more credible than threats to bring about the destruction of civil society on both sides.” By aligning its nuclear war plans with the same moral guidelines that shape its conventional military operations, the United States conveys its resolve to its adversaries and allies.

Given both the risk of conflict involving nuclear-armed states, as well as growing international pressure for nuclear disarmament, U.S. officials need to publicly make their case about the alignment of nuclear policy with the law of armed conflict. Current USSTRATCOM commander General John Hyten made a start in this direction, recently noting his extensive training in law of armed conflict issues: necessity, distinction, proportionality, and unnecessary suffering. He also made clear his obligation to resist orders to use nuclear weapons that fail to comport with the law of armed conflict. More public discussions like this are necessary to reassure the U.S. domestic population about the soundness of their government’s policies, remind them why these weapons exist in the U.S. arsenal, and reinforce the credibility of the U.S. nuclear deterrent. By ensuring that other countries see the United States as willing and able to use its nuclear weapons within its own moral framework, the ultimate risk of nuclear conflict is reduced.

The views expressed are those of the author and do not necessarily reflect the official policy or position of the Department of the Air Force or the U.S. Government.

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