Nuclear Weapons and Customary International Law: A Basic Analysis

Nikhil Dongol

Kathmandu School of Law, Nepal.



A nuclear weapon is an explosive device whose energy results from nuclear reactions, either nuclear fission chain reactions (atomic bomb) or combined nuclear fission and fusion reactions (thermonuclear/hydrogen bomb). By its very nature, that process, in nuclear weapons as they exist today, releases not only immense quantities of heat and energy but also powerful and prolonged radiation which separate it from other conventional weapons. They have the potential to destroy al1 civilization and the entire ecosystem of the planet. Similarly, customary international law refers to the body of the law creating legal obligations binding on a state in its relationships with other states.[1] It is regarded as one of the important sources of international law. Owing to the status on the prohibition on nuclear weapons being a non-liquet except few instances, this paper describes the regulation and status of nuclear weapons under international law, assessing applicable law as it stands (lex lata) and not as one might wish it to be (lex desiderata). This paper concludes that prospective measures designed to deter the use and proliferation of nuclear weapons is more effective than a decision determining the legality of nuclear weapons.


“Let us remember that you are here not simply to avoid a nuclear nightmare, but to build a safer world for all…”

– UN Secretary-General Ban Ki-moon 2010 NPT Review Conference, 3 May 2010

A nuclear weapon is any device which is capable of releasing nuclear energy in an uncontrolled manner and which has a group of characteristics that are appropriate for use for warlike purposes[2]. The Bangkok, Pelindaba, Rarotonga, and Semipalatinsk Treaties specify that the definition of ‘nuclear weapon’ or ‘nuclear explosive device’ does not include the means of transport or delivery of such a weapon or device ‘if separable from and not an indivisible part of it’. Missiles capable of delivering nuclear weapons are therefore not prohibited by those treaties. Their significance may best be appreciated by the coining of the words kiloton (1000 tons) and megaton (1000000 tons) to describe their blast energy in equivalent weights of the conventional chemical explosive TNT. Among military strategists and planners, the very presence of these weapons of unparalleled destructive power has created a distinct discipline, with its own internal logic and set of doctrines, known as nuclear strategy.[3]

The first nuclear weapons were bombs delivered by aircraft. Later, warheads were developed for strategic ballistic missiles, which have become by far the most important nuclear weapons. Smaller tactical nuclear weapons have also been developed, including ones for artillery projectiles, land mines, antisubmarine depth chargestorpedoes, and shorter-range ballistic and cruise missiles. Later the concepts like intercontinental ballistic missiles (ICBMs), and submarine-launched ballistic missiles (SLBMs) also emerged.

The only countries known to have detonated nuclear weapons—and acknowledge possessing them—are (chronologically by date of the first test) the United States, the Soviet Union (succeeded as a nuclear power by Russia), the United KingdomFranceChinaIndiaPakistan, and North KoreaIsrael is believed to possess nuclear weapons, though, in a policy of deliberate ambiguity, it does not acknowledge having them. GermanyItalyTurkeyBelgium and the Netherlands are nuclear weapons sharing states. South Africa is the only country to have independently developed and then renounced and dismantled its nuclear weapons.

Beyond use, the legality of development, testing, production, stockpiling, and transfer must also be assessed under international law. Arguably, a ban on atmospheric testing of nuclear weapons has now crystallized into customary international law; the same cannot, though, be said so easily with respect to underground testing. Already under the 1959 Antarctic Treaty, any activity involving nuclear weapons, such as their testing, stockpiling, deployment, or launching in or from Antarctica is prohibited; similar provisions apply by treaty to nuclear weapons in outer space or on the sea bed. Every 5 year there is an NPT review conference of all the parties to the NPT. 25 years after its entry into force, NPT has been extended for an indefinite period of time. The decision was reached at the 1995 NPT Review and Extension ConferenceThe Treaty on the Prohibition of Nuclear Weapons[4] (Nuclear Weapon Ban Treaty) was adopted on 7 July 2017 as the first legally binding international agreement to comprehensively prohibit nuclear weapons, with the goal of leading towards their total elimination.

Customary International Law is one of the sources of international law. It derives from treaties, custom, general principles of law recognized by nations, judicial decisions, and scholarly writings. These sources of law reflect the consensus of the international community as to particular rules or practices applicable to foreign relations.[5] Once a principle or rule has become customary international law, all states must abide by that law even if a party abrogates the convention. State practice is evidence of whether usage among states has developed into state practise accepted as law.[6] State practice does not need to be unanimous in order to become a customary rule, but should be extensive and virtually uniform.' [7] Only when states regard the norm as embodying legal obligations requiring compliance does a generally accepted norm ascend to customary international lawThis element of customary international law, known as opinion juris, provides that states conform to a pattern of conduct due to a feeling of obligation.[8]

Nuclear weapons have been used twice in war, both times by the United States against Japan near the end of World War II popularly, known as Hiroshima and Nagasaki bombing of 1945.  The ethics of these bombings are subjects of debate and the legality of nuclear weapons under international law remains hotly contested. There are two thoughts on whether the prohibition on nuclear weapons use ascended to customary international law or not.

Customary International Law Prohibits the Use of Nuclear Weapons

Nuclear Weapons Violate the Prohibition Against Unnecessary Suffering

The use of nuclear weapons involves more force than necessary to weaken the military forces of the enemy violated humanitarian laws.[9]  In the only case reviewing the atomic bombings of Hiroshima and Nagasaki, the Tokyo District Court found that the U.S. use of atomic weapons during World War II violated customary international law by causing unnecessary suffering.[10]

Nuclear Weapons Violate the Prohibition Against Indiscriminate Attacks

Nuclear weapons are per se indiscriminate and, therefore, military advantage can never outweigh humanitarian concerns violating Ar. 48 and 51 of Geneva Protocol I[11].

The Cumulative Effect of Treaties and General Assembly Resolutions Limit Nuclear Weapons Use

Although there is no specific treaty which bans the use of nuclear weapons, one set of treaties provides for restrictions on nuclear weapons use or calls for the complete elimination of nuclear weapons[12], while, other conventions attempt to control and limit the existence of nuclear weapons[13]. The signing of NPT by 191 states is overwhelming support that the prohibition of nuclear weapons and its proliferation has become customary law. The General Assembly has adopted numerous resolutions directly relating to the use of nuclear weapons,[14] and total nuclear disarmament.[15] The UNGA has declared that the use of nuclear weapons is a direct violation of the UN Charter and contrary to the rules of international law and laws of humanity.[16] UNGA also deals with the total prohibition of the use and manufacture of nuclear weapons and weapons of mass destruction of every type, together with the conversion of existing stocks of nuclear weapons for peaceful purposes[17], which was also iterated in para 8-13 of the preamble of Nuclear Weapon Ban Treaty.

The law would not impose particular restrictions on nuclear weapons as a weapon type, but merely consider their use as one element in the use of force equations.[18] Arguably, the same formula also applies to threats (ad Bellum): threatening use of force by nuclear weapons is governed by the same legal framework as threats of the use of force in general. Nuclear Weapons case follows 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 United Nations has sought to eliminate such weapons ever since its establishment. The first resolution adopted by the UN General Assembly in 1946 established a Commission and  decided that the Commission should make proposals for “the elimination from national armaments of atomic weapons and of all other major weapons adaptable to mass destruction.”

A number of multilateral treaties have since been established with the aim of preventing nuclear proliferation and testing while promoting progress in nuclear disarmament. These include the Treaty on the Non-Proliferation of Nuclear Weapons (NPT), the Treaty Banning Nuclear Weapon Tests In The Atmosphere, In Outer Space And Under Water, also known as the Partial Test Ban Treaty (PTBT), and the Comprehensive Nuclear-Test-Ban Treaty (CTBT).

A number of bilateral and multilateral treaties and arrangements seek to reduce or eliminate certain categories of nuclear weapons, to prevent the proliferation of such weapons and their delivery vehicles.  These range from several treaties between the United States of America and Russian Federation as well as various other initiatives, to the Nuclear Suppliers Group, the Missile Technology Control Regime, the Hague Code of Conduct against Ballistic Missile Proliferation, and the Wassenaar Arrangement.[19]

Nuclear-weapons-free zones (NWFZs) provide complementary machinery to other measures of disarmament, non-proliferation of nuclear weapons, and the development of peaceful uses of nuclear energy. Therefore, CIL prohibits the use of nuclear weapons.

CIL Does Not Prohibit the Use of Nuclear Weapons

The International Community Has Not Expressly Accepted a Prohibition on the Use of Nuclear Weapons Through Treaty Law or Custom

The rationale supporting the theory of state sovereignty includes maintaining the integrity of, and respect for, sovereign states[20] which is another custom. After the Peace of Westphalia in 1648 which concluded the Thirty Years War, states considered one another sovereign and equal and assumed that no single state could judge another state's internal policies. The NPT[21] even, guarantees all parties the ‘inalienable right’ to peaceful uses of nuclear technology in Article IV, and, in Article VI, also requires the NWS to ‘pursue negotiations in good faith’ towards the reduction and eventual elimination of nuclear arsenals. Only nine states (P5 nations as well as Democratic People’s Republic of Korea, India, Israel, and Pakistan) possess nuclear weapons, but these states represent almost half the world’s population and more than one quarter of the earth’s land area, consequently developing into a CIL.

Policies of Deterrence Have Prevented an Armed Conflict

The reasoning of this doctrine is that the threat of nuclear retaliation will deter a potential aggressor. By adopting policies of deterrence with respect to nuclear weapons, the nuclear weapons states have indicated that they do not accept a per se prohibition on the use of nuclear weapons. The practices and policies of the five nuclear weapons states comprise evidence of state practice relating to the legality of nuclear weapons. By incorporating nuclear weapons into policies of deterrence since 1945, state practice indicates that the international community has not yet accepted a ban on nuclear weapons use.

Nuclear Weapons per se do not violate the distinction between combatants and non-combatants

The doctrine of military necessity justifies the incidental deaths or collateral damage of civilians within the zone of military operations while a state attempts to weaken the enemy's forces. The absence of a treaty specifically prohibiting nuclear weapons use in all circumstances, including self-defense when the survival of the state is at stake as stated in Nuclear Weapons Case[22], suggests that customary international law does not contain a per se prohibition against nuclear weapons use. Furthermore, in the Nicaragua case[23], it has stated that there is no international law which limited the level of armaments of a sovereign state.

Prohibitions on Traditional Methods of Warfare and Conventional Weapons Do Not Necessarily Apply to the Nuclear Age

Hence, there is neither in customary nor conventional law 'any specific authorization of the threat or use of nuclear weapons, but also no comprehensive and universal prohibition against the use of nuclear weapons.[24]


The prohibition distinguishes the NWFZ treaties from the NPT, which does not prohibit the presence of nuclear weapons on the territory of NNWS, providing they do not acquire control over them.[25] NPT only disregard the proliferation of such weapons. In contrast, the Treaties of Bangkok, Pelindaba, Rarotonga, Semipalatinsk, and Tlatelolco prohibit the presence of nuclear explosive devices within the zones, regardless of which state owns or controls them. Furthermore, NPT of 1968 contains only partial prohibitions, and nuclear-weapon-free zone treaties prohibit nuclear weapons only within certain geographical regions. So, The Treaty on the Prohibition of Nuclear Weapons (Nuclear Weapon Ban Treaty) was adopted on 7 July 2017 as the first legally binding international agreement to comprehensively prohibit nuclear weapons, with the goal of leading towards their total elimination. For those nations that are party to it, the treaty prohibits the development, testing, production, stockpiling, stationing, transfer, use and threat of use of nuclear weapons, as well as assistance and encouragement to the prohibited activities. For nuclear-armed states joining the treaty, it provides for a time-bound framework for negotiations leading to the verified and irreversible elimination of its nuclear weapons program. However, its enforcement mechanism is yet to come.

Disarmament obligations on the nuclear weapons states remain contested and remain challenging to enforce. Unless the international community acts prospectively to implement a transparent regulatory system, states will continue to circumvent the existing proliferation regime and will justify nuclear weapons use on grounds of deterrence and self-defence.


[1] Jill M. Sheldon, 'Nuclear Weapons and the Laws of War: Does Customary International Law Prohibit the use of Nuclear Weapons in all Circumstances?' (1996) 20 Fordham International Law Journal 23.

[2] Treaty for the Prohibition of Nuclear Weapons in Latin America (adopted 15 February 1967 come into effect 22 April 1968) 634 UNTS 326 (Tlatelolco Treaty) art 5.

[3] Robert S. NorrisThomas B. Cochran, 'Nuclear Weapons'  <> accessed on 15/4/2018.

[4] Treaty on the prohibition of Nuclear Weapons (adopted 20 September 2017 not entered into force yet) 1155 UNTS 331 (Nuclear Weapons Ban Treaty).

[5] Ian Brownlie, Principles of Public International Law (4th ed., OUP, 1990) 2.

[6] Sir Gerald Fitzmaurice, 'The Law and Procedure of the International Court of Justice, 1951-54: General Principles and Sources of Law' (1953) 30 British Year Book of International Law 55.

[7] North Sea Continental Shelf (F.R.G. v. Den., F.R.G. v. Neth.) (Merits) [1969] ICJ Rep 3, 43 .

[8] Ibid 44.

[9] Protocol Additional to the Geneva Conventions of 12 August 1949, and relating to the Protection of Victims of International Armed Conflicts (adopted 8 June 1977 entered into force 7 December 1978) 1125 UNTS 3 (API) art 35(2); Convention (IV) respecting the Laws and Customs of War on Land and its annex: Regulations concerning the Laws and Customs of War on Land (adopted 18 October 1907 entered into force 26 January 1910) 6 UNTS 3316 (Hague Regulations) art 23(e).

[10] Shimoda v. State (Japanese Government), 8  Japan Annual of International Law 212, 242 (Tokyo Dist. Ct. 1964).

[11] Geneva Protocol 1 (n 9) art 48, 51 .

[12] Five treaties establishing NWFZs have been concluded so far: the 1967 Treaty of Tlatelolco for the Prohibition of Nuclear Weapons in Latin America and the Caribbean, the 1985 Treaty of Rarotonga on the South Pacific NWFZ, the 1995 Bangkok Treaty on the South-East Asia NWFZ, the 1996 Pelindaba Treaty on the African NWFZ, and the 2006 Semipalatinsk Treaty on an NWFZ in Central Asia. All five treaties have entered into force. Mongolia has also unilaterally declared itself a nuclear weapon-free state while Antarctica is free of weapons of mass destruction (WMDs) as a consequence of the 1959 Treaty cited above. By ratifying a NWFZ treaty, states first of all commit themselves not to possess or accept on their territory ‘nuclear weapons’ or ‘nuclear explosive devices’. Article VII of the NPT supports the establishment of nuclear-weapons-free zones (NWFZs) as a regional component of the non-proliferation regime. According to the UN General Assembly 3472(XXX)B, an NWFZ has two essential components: the total absence of nuclear weapons within the zone and the presence of an international verification and control machinery.

[13] Treaty Banning Nuclear Weapon Tests in the Atmosphere, in Outer Space and Under Water (adopted 5 August 1963 entered into force 10 October 1963) 480 UNTS 43 (Partial Test Ban Treaty); Comprehensive Test Ban Treaty ( adopted 10 September 1996 not yet entered into force ) 35 ILM 1439 (CTBT).

[14] UNGA Res 1653 (XVI) (24 November 1961) para 1 (b) (c); UNGA Res 39/148D (17 December 1984) paras 3, 4.

[15] UNGA Res 50/70C (12 December 1995) para.(a) (c); UNGA res 50/70P (12 December 1995) para 1, 4; UNGA Res 50/71E (12 December 1995) para 1; UNGA Res 37/100C (13 December 1982), para 1.

[16] UNGA Res 1653 (XVI) (24 November 1961) para 1(a)(b); Dissenting Opinion of Judge Oda, Legality of the Threat or Use of Nuclear Weapons (Advisory Opinion) [1996] ICJ Rep 94, para 16.

[17] UNGA Res808(IX) A  (4 November 1954)  para 1(b).

[18] Geneva Academy, 'Nuclear Weapons Under International Law: Overview' (2014) 2. [19] UNODA, Nuclear Weapons <> accessed on 15/4/2018.

[20] UN Charter art 2(1).

[21] Treaty on the Non-Proliferation of Nuclear Weapon (adopted 1 July 1968 entered into force 5 March 1970) 729 UNTS 161.

[22]Legality of the Threat or Use of Nuclear Weapon, Advisory Opinion [1996] ICJ Rep 94, para. 96.

[23] Case concerning military and paramilitary activities in and against Nicaragua (Nicaragua v. United States of America) (Merits) [1986] ICJ Rep 392, para 269, p. 135.

[24] Nuclear Weapons Case (n 22), para 95.

[25] For instance, about ninety nuclear warheads are thought to be stationed in the US Ghedi Torre and Aviano military bases in Italy.

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