International Law and Nuclear Weapons

International law regulates the relations among states in times of peace as well as war. International law applies whether a state is democratic or totalitarian. Dictatorships, such as former Nazi Germany and today’s North Korea are bound by international law. Unlike national jurisdiction, international law often lacks control mechanisms and sanctions to guarantee states’ observance. Control mechanisms and sanctions are usually spelled out in treaties.

International law consists of both customary law and treaty law. Customary law is binding on all States, whether or not they have signed a certain treaty. Treaty law is based on conventions (i.e. treaties each state has signed and ratified).

Treaty law is based on conventions – i.e. legal instruments each participating state has signed and ratified. Humanitarian law – rules about the protection of civilians and behavior toward combatants during and after armed conflict – is part of international law and has a special designation—international humanitarian law (IHL). For example, according to IHL, weapons may not be used that cause unnecessary harm to civilians.

Nuclear weapons cannot distinguish between civilians and soldiers. Nuclear weapons will cause massive, indiscriminate damage to military headquarters and village shops, and will kill people whether or not they wear a uniform. The International Court of Justice issued an advisory opinion on 8 July 1996 that the use and threat of use of nuclear weapons violate the principles of international law, and concluded unanimously that all states have an obligation to commence and conclude negotiations on complete nuclear disarmament. Nevertheless, there is no international convention banning nuclear weapons.

The increasing importance of international law

Customary law and treaty law are both important with regard to nuclear weapons. Disarmament treaties aim at protecting states and preventing armed conflicts.

The Geneva Conventions—comprising four treaties and three protocols, the first of which date back to 1864—establish the norms of international humanitarian law (IHL). These agreements, which have been ratified in whole or in part by 196 countries since the end of World War II, define the rights of prisoners of war, afford a variety protections to non-combatants, including doctors and other medical workers, and create a category of war crimes for especially serious violations. While the Geneva Conventions do not ban any particular weapons of war, they establish norms related to proportionality, and the legal use of force in armed conflict. The International Committee of the Red Cross in Geneva is the repository for IHL and maintains extensive databases of all documents related to IHL.

There is an obvious connection between humanitarian law and disarmament law. The Convention on the Prohibition of the Use, Stockpiling, Production and Transfer of Anti-Personnel Mines and on Their Destruction (the Mine Ban Treaty), for example, bans the use of landmines, as these weapons by their very nature violate provisions of IHL.

Nuclear weapons – how are they regulated?

No international convention explicitly bans possession, manufacture, and use of nuclear weapons. The issue of the illegality of nuclear weapons, despite the lack of a convention, was considered by the International Court of Justice (ICJ) in an advisory opinion in 1996.

In this chapter you will find information about most of the conventions that apply to nuclear weapons and about the negotiations leading up to today’s regulations. As you will see, the conventions vary in their degree of detail. Different treaties have different effects.

In some cases, the conventions totally lack control mechanisms, as was the case with the Strategic Offensive Reductions Treaty (SORT) of 2002. States can also withdraw from treaties. In 2002, the US withdrew from the 1972 ABM Treaty, which aimed at preventing development of missile shields. North Korea announced its withdrawal from the Non-Proliferation Treaty in 2003.

Using international law

Both States and the general public can call attention to infringements of international law. The lack of available sanctions in cases where international law is breached, however, can be a problem. Even when the international community provides clear evidence that the government of a country is violating international law (e.g., in the way it treats its citizens), enforcing the norms can be difficult.

International law can also be used as a peace making instrument through the accumulation of conventions, including disarmament agreements. Unfortunately, the nuclear-weapon states have shown an obvious lack of political will to strengthen the peace-building potential of international law by banning and abolishing nuclear weapons.

The ICJ advisory opinion

On 8 July 1996, the International Court of Justice (ICJ) in The Hague published an advisory opinion about the legality of use of nuclear weapons. The ICJ had been asked by the UN General Assembly whether the use of nuclear weapons violates international law.

The ICJ responded that in most cases the threat or use of nuclear weapons does violate international law. The use of nuclear weapons is illegal because they cannot distinguish between soldiers and civilians or between civilian and military targets. A nuclear attack will cause indiscriminate harm, killing both civilians and soldiers.

Nuclear weapons are also illegal because they cause unnecessary suffering. According to international law, warring parties may only use as much force as is needed to achieve a legitimate military objective. This is called the principle of proportionality. States outside the armed conflict must also not be affected by the use of violence—a condition that cannot be met if nuclear weapons are used. States that are not parties to the conflict will be severely harmed not only by the radioactive fallout that spreads over large areas following a nuclear explosion but also, as we have learned in recent years, by the global climate disruption and nuclear famine that would result from a limited, regional nuclear war using only a small fraction of the nuclear weapons that exist today. 

International law prohibits states from initiating armed violence against other states, although a country that has been attacked has the right to self-defense. The ICJ was asked whether a state can use nuclear weapons in self-defense even if the use of nuclear weapons is illegal in most cases.

The Court was unable to reach a conclusion about the legality of the use of nuclear weapons in the extreme situation when a country’s existence is threatened. The ICJ stated, however, that ”the 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”.

The ICJ further stated in its advisory opinion that all States have an obligation to complete the task of nuclear disarmament. The Court referred to Article VI the NPT, which deals with nuclear disarmament, and noted that all Member States are obliged to negotiate and complete the task of nuclear disarmament.


Last update: August 24, 2015