For over fifty years, the legality of nuclear weapons has been one of the most emotional and intellectually divisive issues in the laws of war. Eminent experts in international law can be found on both sides of the question.

Those supporting the legality of nuclear weapons argue that such weapons can be used in accordance with the laws of war. The United States government, for example, has for thirty years claimed that it recognizes the following legal principles as applying to the use of nuclear weapons: that the right of the parties to a conflict to adopt means of injuring the enemy is not unlimited; that it is prohibited to launch attacks against the civilian population as such; and that distinction must be made at all times between persons taking part in hostilities and members of the civilian population to the effect that the latter be spared as much as possible.

Supporters of nuclear weapons argue that the actual practice of States is a more primary source of international law than theoretical legal principles. They note that the five original nuclear powers (United States, Soviet Union/Russia, United Kingdom, France, and China) have deployed nuclear weapons for decades, and have openly claimed the legal right to use these weapons in self-defense. (In 1998, India and Pakistan also openly claimed the right to nuclear weapons.) It has also been pointed out that the 1968 Treaty on the Non-Proliferation of Nuclear Weapons (the NPT) expressly recognizes the legal right of the five original nuclear powers to possess nuclear weapons. Over 170 countries are parties to the NPT.

Those opposing the legality of these weapons include a number of nongovernmental organizations (NGOs), such as the International Committee of the Red Cross (ICRC), which expressed reservations, as well as some governments. They tend to base their arguments on the general humanitarian principles underlying the laws of war. For opponents, the vast destructive power of nuclear weapons makes a mockery of efforts to protect hospitals, the sick and wounded, civilians, and others as required by these humanitarian principles. Civilians may be spared “as much as possible” in a nuclear war, but in practice, they believe, it will be possible to spare very few. The civilian casualties and environmental damage will inevitably be disproportionate to the value of the military targets that nuclear weapons destroy.

In 1994, several NGOs opposed to the use of nuclear weapons convinced a majority of the United Nations General Assembly to ask the International Court of Justice at The Hague for an advisory opinion on the legality of nuclear weapons and their use. Under the UN Charter, the General Assembly is authorized to request such an opinion from the court on any legal question. (The United States opposed adoption of the resolution but was outvoted.) The court’s opinion, delivered on July 8, 1996, illustrates how deeply divided the international legal community is on this issue. The fourteen judges then sitting on the court split evenly on whether nuclear weapons could ever be lawfully used in accordance with the laws of war. In that situation, the president of the court is allowed to cast a second vote to break the tie. By this procedure, the court gave the General Assembly the following ambiguous advice:

“[T]he threat or use of nuclear weapons would generally be contrary
to the rules of international law applicable in armed conflict, and in
particular the principles and rules of humanitarian law;

“However, in view of the current state of international law, and of the elements of fact at its disposal, the Court cannot conclude definitively whether the threat or use of nuclear weapons would be lawful or unlaw- ful in an extreme circumstance of self-defense, in which the very survival of a State would be at stake.”

(See indiscriminate attack; military necessity; proportionality.)