Key nuclear arms control agreements

Quite a few nuclear arms control agreements have been negotiated over the last half-century. Some have been signed by a large number of countries, others by just two. Here are the most important agreements:

Multilateral treaties

Arms control agreements aimed at a membership by as many states as possible, or even universal membership, tend to be the most important. A number of them primarily serve to prevent the spread of nuclear weapons and the emergence of new nuclear powers, although such non-proliferation agreements also profess the longer-term goal of nuclear disarmament.

The Nuclear Non-Proliferation Treaty (NPT)

The agreement of greatest political weight is the Non-Proliferation Treaty (NPT). Adopted in 1968 and entering into force in 1970, the Treaty has since been joined by almost every country on Earth. It was originally set to run only for a term of 25 years, but this provision was rescinded in 1995. The NPT recognizes just five states as members with nuclear-weapon status: China, France, United Kingdom, Russia and the United States. All the other members are non-nuclear states parties. The only non-members today are India, Israel, Pakistan and, since 2003, North Korea, although the latter’s treaty withdrawal is not internationally recognized. Every one of these non-members is known to be actively pursuing military nuclear programmes and may only join the Treaty if they first renounce such programmes.

Under Article 2 of the NPT, the non-nuclear treaty members undertake “not to manufacture or otherwise acquire nuclear weapons or other nuclear explosive devices; and not to seek or receive any assistance in the manufacture of nuclear weapons or other nuclear explosive devices.” Conversely, the five recognized nuclear-weapon states pledge under Article 1, never to assist non-nuclear parties in evading their commitment under Article 2. In return, Article 4 of the Treaty guarantees non-nuclear parties the right to the fullest civil-only use of nuclear technology, including facilities for a closed fuel-cycle with enrichment and reprocessing. “Nothing in this Treaty shall be interpreted as affecting the inalienable right of all Parties to the Treaty to develop research, production and use of nuclear energy for peaceful purposes ….” Indeed, the parties are guaranteed international assistance in these efforts.

In this way, the Treaty distinguishes between the group of five long-standing powers with nuclear weapons, regarded as legitimate holders, and all the remaining treaty members without nuclear weapons. Yet, it does place obligations on the former group. Article 6 requires of each nuclear-weapon member that it “undertakes to pursue negotiations in good faith on effective measures relating to cessation of the nuclear arms race at an early date and to nuclear disarmament, and on a treaty on general and complete disarmament under strict and effective international control.”

The NPT thus rests on a swap: One group pledges to follow the imperative on non-proliferation, while the other promises to move towards complete nuclear disarmament and return to the status of non-nuclear weapon state. Discussions at the review conferences have highlighted the line that divides the nuclear haves and have-nots. While the nuclear-weapon states and their allies call for stricter non-proliferation rules and better inspection regimes, the non-nuclear members on the other side regularly demand binding and more comprehensive disarmament commitments on the part of the nuclear powers. If the two sides continue to disagree, the review conferences mark a failure, as occurred in 2005 under US President George W. Bush.

The test ban treaties

The Treaty Banning Nuclear Weapon Tests in the Atmosphere, in Outer Space and under Water entered into force in 1963, giving the international community a multilateral instrument for preventing all nuclear weapons tests not carried out underground. This agreement is also referred to as the Partial Test Ban Treaty (PTBT) or the Limited Test Ban Treaty (LTBT). A common position on testing was originally reached through negotiations between the United Kingdom, the United States and the Soviet Union. To date, some 130 nations have joined the Treaty, while ten others have signed it but not yet ratified. Although there are some important non-members, like China or France, they are still complying with its provisions. The United States and the Soviet Union went beyond the partial test ban in 1974 by concluding a bilateral agreement to rule out subterranean nuclear tests with yields in excess of 150 kilotons. This is known as the Threshold Test Ban Treaty (TTBT).

A Comprehensive Nuclear-Test-Ban Treaty (CTBT) was opened for signature in 1996, proscribing nuclear tests completely. By 2017, 183 countries had signed, and 166 had ratified, but the CTBT has still not entered into force because it has not been ratified by all of the 44 states listed in the annex in 1996. Three of those states, namely India, Pakistan and North Korea, have continued to test nuclear weapons since 1995.

Nuclear-weapon-free zones

Multilateral nuclear arms control agreements also include arrangements for zones without nuclear weapons. Under all these zone treaties, the states parties undertake to not to possess or stockpile any nuclear weapons on their sovereign territory. . The Treaty of Tlatelolco (Latin America, Caribbean) has 33 member nations, the Treaty of Roratonga (South Pacific) thirteen, the Treaty of Bangkok (Southeast Asia) ten and the Treaty of Semei (Central Asia) five. The Treaty of Pelindaba, adopted in 2006, has been signed by 54 African countries and has now entered into force, although not all member states have completed ratification. The UN recognizes one additional country, Mongolia, as a zone with nuclear-free status. Antarctica also shares this status inasmuch as the Antarctic Treaty, with its 45 states parties, outlaws the stationing of nuclear weapons in that region. Moreover, the international community has also concluded a treaty-based ban on the stationing of nuclear weapons on the seabed. To signal their support for the existence of nuclear-weapon-free zones, the nuclear weapon states have issued “negative security assurances”, pledging neither to use nuclear weapons against any territory of zone members nor to threaten them with such weapons.

Bilateral agreements to contain nuclear weapons capabilities

From the late 1960s, Moscow and Washington began to look for a way of containing a nuclear arms race that had spun out of control. After the Cuba missile crisis, the two superpowers became interested in arms control agreements that would offer qualitative and quantitative containment and stabilize the system of mutual deterrence in the event of further crises. Even though the two sides had very different interests in detail due to the asymmetry in their nuclear capabilities, and even though both were seeking to gain an advantage, the United States and the Soviet Union shared an interest in finding a compromise aimed at stabilizing the deterrence system on the basis of mutually assured destruction. Furthermore, having signed the NPT in 1968, both powers had a common desire to take their disarmament commitments under that Treaty at least serious enough to prevent further proliferation of nuclear weapons worldwide.


The Anti-Ballistic-Missile (ABM) Treaty came into being in May 1972. Its aim was to guarantee that the two superpowers would both remain vulnerable to nuclear attack, thus maintaining effective “deterrence”. It allowed each side two, and from 1974 just one, local missile defence system with a maximum of 100 missile interceptors. This was to ensure that both sides remained vulnerable.

In the same year, an interim agreement was signed after the Cold War superpowers completed a negotiating process called SALT (Strategic Arms Limitation Talks. The talks resulted in an interim agreement, SALT-1, on a five-year freeze on the number of strategic ballistic missile delivery systems (land and sea-launched ballistic missiles as well as heavy bomber aircraft) deployed by the United States and the Soviet Union. The agreement prevented a further quantitative build-up of arms and also restrained qualitative advances in their destructive potential. It was also foreseen that negotiations would soon move on to arrangements to reduce the superpowers’ offensive strategic nuclear capabilities.

Since, as is so often the case, the devil was in the detail, it took seven years and 130 rounds of talks between the two nuclear adversaries, the United States and the Soviet Union, until, in June 1979, such an agreement was ready for signing in the shape of SALT-2. It allowed the superpowers to initially have a maximum of 2,400 strategic launch systems each, to be scaled down to 2,250 systems by 1 January 1982. Although the SALT II agreement never came into force because the US Senate would not ratify it, both sides did, in fact, observe the provisions.


On 31 July 1991, after the end of the Cold War, Moscow and Washington agreed a follow-up treaty known as START, the Strategic Arms Reduction Treaty, which laid down more significant reductions to their nuclear arsenals, which still amounted to more than 10,000 nuclear warheads on either side. START set an arms reduction target to be reached within seven years of the treaty becoming effective. Each side was allowed (on 5 December 1994) to possess no more than 1,600 “strategic nuclear delivery vehicles” and 6,000 active warheads for these systems. Moreover, the treaty contained a number of supplementary provisions on specific aspects, including reciprocal on-site inspection protocols. The treaty was due to run until December 2009.

Even before the initial treaty had come into force, a follow-up agreement was signed by both sides on 3 January 1993. Called START II, the treaty focused on the danger of multiple independently targetable warheads. It required the deactivation of all land-based intercontinental missiles with multiple warheads and steps to reduce the number of delivery-attributed operational warheads permissible by the end of 2002 to between 3,000 and 3,500 warheads. In 1997, the deadline was extended to the end of 2007. START II was ratified by the United States in 1996, while endorsement from the Russian Parliament was not received until 2000. Yet START II never entered into force because the Duma had made continuation of the ABM Treaty a precondition for its acceptance, while the United States revoked the ABM Treaty in 2002—a Treaty regarded by Russia as underpinning the whole system of SALT and START arrangements.

Nevertheless, a further reduction in the number of permissible warheads on strategic delivery systems was agreed in May 2002 with the signing of the Strategic Offensive Reductions Treaty (SORT), also known as the Treaty of Moscow. Here, Russia and the United States undertook to reduce their warhead numbers to between 1,700 and 2,200 by the end of 2012.

The ceilings were lowered again in 2010 by New START, a treaty limiting delivery systems to 800 on each side and the assigned warheads to 1,550. The Treaty became effective in February 2011 and is due to run until 2020. Yet another follow-up agreement is being pursued.


The Intermediate-Range Nuclear Forces (INF) Treaty, adopted in 1987, can be seen as a special case. It ended a dispute, running since the second half of the 1970s, on the deployment of modern medium-range and short-range nuclear weapons by the Soviet Union and the United States respectively across Europe. Under the Treaty, each side undertakes not to develop, possess or deploy land-based nuclear weapons with a range of 500 to 5,500 kilometres. It thus eliminated for the first time a whole category of nuclear arms. A peculiarity of the Treaty was the involvement of a non-nuclear-weapon state, the Federal Republic of Germany, which possessed the necessary delivery systems. Without itself being a party to the Treaty, West Germany unilaterally declared it would have its 72 Pershing IA missiles scrapped.

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