Does the Legality of Nuclear War Matter?


Seventy years ago, Japan offered its unconditional surrender to the United States and Allied Powers. The surrender was predicated, at least in part, on the first usage of nuclear weapons in war. The two U.S. nuclear detonations over Hiroshima and Nagasaki helped convince the Japanese strategic leadership defeat was inevitable and broke the empire’s will to fight. In addition to being the first time nuclear weapons have been used in conflict, it was also the last, even as there are now at least nine states confirmed or suspected to possess nuclear weapons. As the U.S. Congress debates the viability and wisdom of an agreement intended to stop Iran from becoming the world’s tenth nuclear-armed state, it is worth considering the political and legal context of nuclear weapons in the modern international order.

In 1996, the United Nations General Assembly referred to the International Court of Justice (ICJ) — the principal judicial organ of the United Nations — a request for an “advisory opinion” relating to the legality of the use nuclear weapons. Advisory opinions are relatively rare in both domestic and international jurisprudence, as one fundamental principle of judicial power is that judges usually only consider cases that decide a concrete issue between two or more opposing parties. Advisory opinions are bare exercises in judicial pontification and it is more difficult to take seriously a judicial pronouncement in a vacuum than when it actually decides a case. Even so, the ICJ accepted the invitation to opine on the question and issued the most definitive, if imperfect, legal guidance on the use of nuclear weapons in modern international jurisprudence. While not the only source of international law, ICJ rulings and other international judicial opinions are highly influential in terms of restating binding principles of international law.

The advisory opinion, “Legality of the Threat or Use of Nuclear Weapons,” applied concepts of both jus ad bellum (right to war) and jus in bello (the conduct of warfare), the law of neutrality, and specific conventions and treaties directly germane to nuclear weapons.

In terms of jus ad bellum the ICJ noted the Articles of the United Nations Charter dealing with the use of force and self-defense do not refer to specific types of weapons, and apply to all weapons, subject to the usual restraints under the law of armed conflict of necessity and proportionality. The court noted mere possession of a nuclear weapon does not amount to a per se unlawful “threat” of force under international law. The court looked at whether there are specific, special rules applying to nuclear weapons, and found no specific restrictions related to the particular type of weapon. Nonproliferation treaty law is ascendant in the modern era, the court noted, but the body of treaty law does not yet constitute a proscription on the weapons. The court also found no customary international law prohibition arising from non-use after Hiroshima and Nagasaki. Non-use by states since 1945 could constitute a customary prohibition if it was also accompanied by opinio juris — beliefs by states that non-use was required by law. However, no such belief by states exists, as the nuclear powers clearly believe use is a viable strategic option. Otherwise, the states would not own, deploy, maintain, and train on the use of the weapons.

On the subject of jus in bello, the ICJ keyed in on the principles of distinction — targeting legitimate military objects of attack, rather than protected civilians — and unnecessary suffering as key international law considerations pertaining to the conduct of hostilities using nuclear weapons. The court found nuclear weapons’ extreme destructive nature made their use irreconcilable with the requirements of international humanitarian law — the law of armed conflict — but left open the possibility the weapons might be allowable in an extreme case of self-defense in which the state’s very survival is at stake.

The 1996 ICJ opinion restricted significantly the legality of the use of nuclear weapons to certain narrow self-defensive circumstances implicating state survival. If the advisory opinion’s analysis is the last word on the legality of the military use of nuclear weapons, it suggests a real and substantial legal and political restraint on the use of nuclear weapons in combat. If this analysis had been applied retroactively to the Hiroshima and Nagasaki attacks — which killed 150,000 and 75,000 civilians, respectively — it would be difficult to imagine an international court finding that the United States sufficiently honored the principles of distinction and prevention of unnecessary suffering. Moreover, the United States would also have had to show that it suffered under an existential threat. By 1945 — with Japan suffering a series of naval and land defeats — the existential threat posed by Japan was probably lower than at any point in the war.

Nevertheless the political effect of the advisory opinion’s issuance was to confirm the ambiguity surrounding the issue. The court was unwilling to lay down a bright line rule regarding the legality of the use of nuclear weapons in self-defense, leaving open the possibility of a lawful and politically legitimate use of nuclear weapons in particularly dire circumstances. The ICJ’s opinion helped confirm the continued viability of nuclear arsenals as an element of statecraft, and bolstered the political standing of nuclear states. Finally, the court was likely cognizant of the fact that an opinion making nuclear use unlawful in all circumstances would be roundly ignored by the nuclear states: The United States and Russia would not surrender their nuclear arsenals because a handful of foreign judges implied they should.

Twenty-five countries testified in the case and 30 states, including confirmed nuclear powers the United States, the United Kingdom, France, Russia, and India, submitted written materials, demonstrating the international buy-in to the court’s legitimacy and the stakeholders’ interest in the outcome. An opinion completely outlawing nuclear weapons would have been flouted, damaging the court’s credibility and authority in future cases. The international community largely welcomed the opinion: Non-nuclear states were forced to acknowledge the restraints the court placed on the nuclear powers, and nuclear powers escaped with their authority to use nuclear weapons in extreme situations largely intact.

In light of the changes in the international order since 1996, what result would occur if the ICJ were asked to reconsider its opinion today? In 1996, the Soviet Union had only recently collapsed and Russia’s resurgence was uncertain. Russia has since demonstrated its willingness to flex military muscle. Its leadership has also engaged in regular nuclear sabre rattling in the last two years. China’s military power is stronger than ever, as it also demonstrates willingness to exercise regional hegemony over its near abroad, and its alacrity for engaging in cyberattacks and cyberespionage are well known. Iran has become a nuclear threshold state and may continue to strive for a nuclear weapon, North Korea has tested multiple weapons, and Israel — widely seen as a nuclear power — perceives itself constantly on the edge of existential threats. Pakistan and India are both nuclear-armed and continue to foment hatred for each other that has led to multiple conflicts and skirmishes since Partition in 1947. The court would also need to contend with changes in the international legal environment. Have the effects of conflicts on civilians in the Balkans, Iraq, Afghanistan, Africa, and South Asia, for example, changed the political calculus such that the massive civilian casualties attendant to use of a nuclear weapon would be deemed unacceptable, unlawful, and therefore politically illegitimate? Would the ICJ apply human rights law to augment a more traditional international humanitarian (law of armed conflict) analysis? The emerging trend of international legal scholars and courts comingling the bodies of international humanitarian law and international human rights law, would leave the court unlikely to find the use of nuclear weapons lawful under any circumstance. Has the rate of change in the way the international community views warfare accelerated, such that the risk of condemnation of the use of nuclear weapons gets more likely as time goes on? Finally, in the wake of the use of a nuclear weapon, or a nuclear exchange, is the legality of use even particularly relevant? Wouldn’t the international community have so much more to worry about in terms of de-escalation and consequence management, relegating legal and political legitimacy to historians to sort out after the fact?

The seven-decade anniversary provides context for consideration of what has changed in the intertwined political and legal landscape since 1945 and again since 1996 regarding the use of nuclear weapons in armed conflict. The concepts of military commissions and indefinite detention of enemy combatants provide a useful parallel. These practices were relatively uncontroversial in World War II, but more recently in history, they produced constant litigation, intra-governmental investigations, and political turmoil. Between World War II and the 2002 opening of a prison for enemy combatants in Guantanamo, perceptions of military commissions and indefinite detention, and society as a whole, changed dramatically. The progenitors of today’s commissions and detention architecture may not have appreciated these tectonic political, social, and legal shifts, particularly the growth of judicially recognized civil rights in the 1950s and 1960s. Similarly, the ICJ’s 1996 opinion conveys a lot about the political and legal factors at play with regard to the use of nuclear weapons, but may be sufficiently dated that a different outcome could result in 2015. Indefinite detention has proven to be a political thorn in the side of the United States in the international political community, which theoretically could subject political leaders to international criminal jurisdiction. Similarly, illegal use of nuclear weapons could have a political and legal effect on the United States far in excess of any consequences surrounding the policies of indefinite detention and abuse of detainees.


Butch Bracknell is a retired Marine officer and international lawyer. He is a member of the Truman National Security Project’s Defense Council and the University of Virginia’s Sorensen Institute of Political Leadership.