Nuclear Treaties
and Agreements

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Throughout the history of nuclear weapons, arms control treaties and agreements and nonproliferation efforts have been used to promote and implement U.S. national security objectives. The United States engages in arms control arrangements when they serve U.S. national security. Arms control and nonproliferation efforts have produced formal treaties and agreements, informal arrangements, cooperative threat reduction and monitoring mechanisms, and consultation summits. The United States and the Soviet Union began to sign agreements limiting their strategic offensive nuclear weapons in the early 1970s. While several arms control agreements restrict the deployment and use of nuclear weapons, no conventional or customary international law prohibits nations from employing nuclear weapons in armed conflict. This chapter describes the treaties and international agreements that have affected the size and composition of the U.S. nuclear weapons stockpile as well as those that promote the goals of nuclear nonproliferation.

List of Nuclear-Related Treaties and International Agreements

Antarctic Treaty
Opened for signature: 1959| Entry into force: 1961

Treaty Banning Nuclear Weapon Tests in the Atmosphere, in Outer Space and Under Water (Limited Test Ban Treaty or LTBT)
Opened for signature: 1963|Entry into force: 1963

Treaty for the Prohibition of Nuclear Weapons in Latin America (Treaty of Tlatelolco)
Opened for signature: 1967|Entry into force: 1968

Treaty on the Nonproliferation of Nuclear Weapons (Nuclear Nonproliferation Treaty or NPT)
Opened for signature: 1968|Entry into force: 1970

Treaty Between the United States of America and the Union of Soviet Socialist Republics on the Limitation of Anti-Ballistic Missile Systems (Anti-Ballistic Missile Treaty or ABM Treaty)
Signed: 1972|Entry into force: 1972|U.S. Withdrawal: 2002

Interim Agreement Between the United States of America and the Union of Soviet Socialist Republics on Certain Measures with Respect to the Limitation of Strategic Offensive Arms (Strategic Arms Limitation Talks or SALT I)
Signed: 1972|Entry into force: 1972

Treaty Between the United States of America and the Union of Soviet Socialist Republics on the Limitations of Underground Nuclear Weapon Tests (Threshold Test Ban Treaty or TTBT)
Signed: 1974|Entry into force: 1990

Treaty Between the United States of America and the Union of Soviet Socialist Republics on Underground Nuclear Explosions for Peaceful Purposes (Peaceful Nuclear Explosions Treaty or PNET)
Signed: 1976|Entry into force: 1990

Treaty Between the United States of America and the Union of Soviet Socialist Republics on the Limitation of Strategic Offensive Arms (Strategic Arms Limitation Treaty or SALT II)
Signed: 1979|SALT II never entered into force, although both sides complied with its provisions until 1986

Convention on Physical Protection of Nuclear Materials (CPPNM) and its 2005 Amendment
Signed: 1980|Entry into force: 1986
2005 Amendment adopted: 2005|Entry into force: 2016

South Pacific Nuclear-Free Zone Treaty (Treaty of Rarotonga)
Opened for signature: 1985|Entry into force: 1986

Treaty Between the United States of America and the Union of Soviet Socialist Republics on the Elimination of their Intermediate-Range and Shorter-Range Missiles (Intermediate-Range Nuclear Forces Treaty or INF Treaty)
Signed: 1987|Entry into force: 1988|U.S. Withdrawal: 2019

Treaty Between the United States of America and the Union of Soviet Socialist Republics on the Reduction and Limitation of Strategic Offensive Arms (Strategic Arms Reduction Talks (START) Treaty)
Signed: 1991|Entry into force: 1994

Presidential Nuclear Initiatives (PNI)
Announced: 1991 (The PNI were “reciprocal unilateral commitments” and thus are politically, not legally, binding and non-verifiable)

Treaty on Open Skies
Signed: 1992|Entry into force: 2002

Treaty Between the United States of America and the Russian Federation on Further Reduction and Limitation of Strategic Offensive Arms (START II)
Signed: 1993|START II never entered into force

Treaty on the Southeast Asia Nuclear Weapon-Free Zone (Bangkok Treaty)
Opened for signature: 1995|Entry into force: 1997

African Nuclear Weapon-Free Zone Treaty (ANWFZ or Treaty of Pelindaba)
Opened for signature: 1996|Entry into force: 2009

Comprehensive Nuclear Test-Ban Treaty (CTBT)
Opened for signature: 1996|CTBT never entered into force

Treaty Between the United States of America and the Russian Federation on Strategic Offensive Reductions (Strategic Offensive Reductions Treaty, SORT, or Moscow Treaty)
Signed: 2002|Entry into force: 2003

Central Asian Nuclear Weapon-Free Zone Treaty (CANWFZ)
Opened for signature: 2006|Entry into force: 2009

Treaty Between the United States of America and the Russian Federation on Measures for the Further Reduction and Limitation of Strategic Offensive Arms (New START Treaty)
Signed: 2010|Entry into force: 2011

The Joint Comprehensive Plan of Action (JCPOA) (aka the Iran nuclear deal)
Signed: 2015|United States terminated participation: 2018

Nuclear Weapon-Free Zones

Nuclear Weapon-Free Zones prohibit the stationing, testing, use, and development of nuclear weapons inside a particular geographical region. This is true whether the area is a single state, a region, or land governed solely by international agreements. There are several regional agreements to exclude or preclude the development and ownership of nuclear weapons. These agreements were signed under the assumption that it is easier to exclude/preclude weapons than to eliminate or control them once they have been introduced.

There are six existing Nuclear Weapon-Free Zones (see Figure 12.1) established by treaty: Antarctica, Latin America, the South Pacific, Southeast Asia, Africa, and Central Asia.

Figure 12.1
Figure 12.1 Map of Nuclear Weapon-Free Zones

Antarctic Treaty

Scientific interests rather than political, economic, or military concerns dominated the expeditions sent to Antarctica after World War II. International scientific associations made informal agreements to guide scientific study and cooperation in Antarctica. On May 3, 1958, the United States proposed a conference to consider the points of agreement that had been reached in informal multilateral discussions. Specifically, the conference sought to formalize international recognition that:

  • the legal status quo of the Antarctic Continent would remain unchanged;
  • scientific cooperation would continue; and
  • the continent would be used for peaceful purposes only.

The Washington Conference on Antarctica culminated in a treaty signed on December 1, 1959. The treaty entered into force on June 23, 1961, when the formal ratifications of all participating nations had been received.

The treaty provides that Antarctica shall be used for peaceful purposes only. It specifically prohibits “any measures of a military nature, such as the establishment of military bases and fortifications, the carrying out of military maneuvers as well as the testing of any type of weapons.” Military personnel or equipment, however, may be used for scientific research or for any other peaceful purpose. Nuclear explosions and the disposal of radioactive waste material in Antarctica are prohibited, subject to certain future international agreements on these subjects. There are provisions for amending the treaty, for referring disputes that cannot be handled by direct talks, mediation, arbitration, or other peaceful means to the International Court of Justice, and for calling a conference 30 years post-entry into force to review the implementation of the treaty if any parties so request.

Treaty for the Prohibition of Nuclear Weapons in Latin America (Treaty of Tlatelolco)

The concept of a Latin American Nuclear Weapon-Free Zone was first introduced to the United Nations General Assembly in 1962. On November 27, 1963, this concept was codified and received the support of the U.N. General Assembly, with the United States voting in the affirmative.

On February 14, 1967, the Treaty was signed at a regional meeting of Latin American countries in Tlatelolco, a section of Mexico City. The Treaty entered into force in 1968.

The basic obligations of the Treaty are contained in Article I:

The Contracting Parties undertake to use exclusively for peaceful purposes the nuclear material and facilities which are under their jurisdiction, and to prohibit and prevent in their respective territories: (a) the testing, use, manufacture, production, receipt, storage, installation, deployment, or acquisition by any means whatsoever of any nuclear weapons by the parties themselves, directly or indirectly, on behalf of anyone else or in any other way, and (b) the receipt, storage, installation, deployment and any form of possession of any nuclear weapons, directly or indirectly, by the parties themselves, or by anyone on their behalf or in any other way.

In Additional Protocol II to the Treaty, states outside of Latin America undertake to respect the denuclearized status of the zone, not to contribute to acts involving violation of obligations of the parties, and not to use or threaten to use nuclear weapons against the Contracting Parties.

The United States ratified Additional Protocol II on May 8, 1971, and deposited the instrument of ratification on May 12, 1971, subject to several understandings and declarations. France, the United Kingdom, China, and Russia are also parties to Protocol II.

South Pacific Nuclear-Free Zone Treaty (Treaty of Rarotonga)

On August 6, 1985, the South Pacific Forum, a body comprising the independent and self-governing countries of the South Pacific, endorsed the text of the South Pacific Nuclear-Free Zone Treaty and opened it for signature.

The treaty is in force for 13 of the 16 South Pacific Forum members (Australia, Cook Islands, Fiji, Kiribati, Nauru, New Zealand, Niue, Papua New Guinea, Samoa, Solomon Islands, Tonga, Tuvalu, and Vanuatu). The Federated States of Micronesia, the Marshall Islands, and Palau are not eligible to be parties to the treaty because of their Compact of Free Association with the United States. The United States, United Kingdom, France, Russia, and China have all signed the Protocols that directly pertain to them (France and the United Kingdom have ratified all three protocols. Russia and China have only ratified Protocols II and III). United States ratification of all three protocols is pending.

The parties to the Treaty agreed:

  • not to manufacture or otherwise acquire, possess, or have control over any nuclear explosive device by any means anywhere inside or outside the South Pacific Nuclear-Free Zone;
  • not to seek or receive any assistance in the manufacture or acquisition of any nuclear explosive device;
  • to prevent the stationing of any nuclear explosive device in their territory;
  • to prevent the testing of any nuclear explosive device in their territory; and
  • not to take any action to assist or encourage the testing of any nuclear explosive device by any state.

Treaty on the Southeast Asia Nuclear Weapon-Free Zone (Bangkok Treaty)

Indonesia and Malaysia originally proposed the establishment of a Southeast Asia Nuclear Weapon-Free Zone in the mid-1980s. On December 15, 1995, ten Southeast Asian states signed the treaty on the Southeast Asian Nuclear Weapon-Free Zone at the Association of Southeast Asian Nations (ASEAN) Summit in Bangkok.

The treaty commits parties not to conduct or receive, or to aid in the research, development, manufacture, stockpiling, acquisition, possession, or control over any nuclear explosive device by any means. Each state party also undertakes not to dump at sea or discharge into the atmosphere any radioactive material or wastes anywhere within the zone. Under the treaty protocol, each state party undertakes not to use or threaten to use nuclear weapons against any state party to the treaty and not to use or threaten to use nuclear weapons within the zone. The treaty entered into force in 1997.

The United States has not signed the Protocol to the Bangkok Treaty.

African Nuclear Weapon-Free Zone (ANWFZ) Treaty (Pelindaba Treaty)

The Organization of African Unity (OAU) first formally enunciated the desire to draft a treaty ensuring the denuclearization of Africa in July 1964. No real progress was made until South Africa joined the Nuclear Nonproliferation Treaty (NPT) in 1991. In April 1993, a group of United Nations and OAU experts convened to begin drafting a treaty. The Pelindaba Treaty commits parties not to conduct or receive or give assistance in the research, development, manufacture, stockpiling, acquisition, possession, or control over any nuclear explosive device by any means anywhere.

The Treaty was opened for signature on April 11, 1996, and entered into force on July 15, 2009. The United States, the United Kingdom, France, China, and Russia and Russia have all signed the relevant treaty protocols. The United States has not ratified the treaty.

Central Asian Nuclear Weapon-Free Zone (CANWFZ) Treaty

The concept of a Central Asian Nuclear Weapon-Free Zone (CANWFZ) first arose in a 1992 Mongolian initiative in which the country declared itself a nuclear weapon-free zone and called for the establishment of a regional NWFZ. A formal proposal for a Central Asian Nuclear Weapon-Free Zone was made by Uzbekistan at the 48th session of the United Nations General Assembly in 1993, but a lack of regional consensus on the issue blocked progress on a CANWFZ until 1997. On February 27, 1997, the five presidents of the Central Asian states (Kazakhstan, Kyrgyzstan, Tajikistan, Turkmenistan, and Uzbekistan) issued the Almaty Declaration, which called for the creation of a CANFWZ.

The text of the CANWFZ Treaty was agreed upon at a meeting held in Uzbekistan from September 25–27, 2002. On February 8, 2005, the five states adopted a final draft of the treaty text, and the treaty was opened for signature on September 8, 2006. The treaty establishing the CANWFZ entered into force on March 21, 2009. The United States did not ratify the treaty.

Nuclear Weapons Treaties

Limited Test Ban Treaty

The Treaty Banning Nuclear Weapon Tests in the Atmosphere, in Outer Space and Under Water, or the Limited Test Ban Treaty (LTBT) of 1963, prohibits nuclear weapons tests “or any other nuclear explosion” in the atmosphere, in outer space, and under water. While the treaty does not ban tests underground, it does prohibit nuclear explosions in this environment if they cause “radioactive debris to be present outside the territorial limits of the state under whose jurisdiction or control” the explosions were conducted. In accepting limitations on testing, the nuclear powers accepted as a common goal “an end to the contamination of the environment by radioactive substances.”

The LTBT is of unlimited duration. The Treaty is open to all states, and most of the countries of the world are parties to it. The Treaty has not been signed by France, the People’s Republic of China (PRC), or North Korea.

Nuclear Nonproliferation Treaty

In 1968, the United States signed the Treaty on the Nonproliferation of Nuclear Weapons, often called the Nuclear Nonproliferation Treaty. Most nations of the world are parties to the Treaty; it forms the cornerstone of the international nuclear nonproliferation regime. The NPT recognizes the five nuclear powers that existed in 1968: the United States, the Soviet Union,1 the United Kingdom, France, and China. The Treaty prohibits all other signatories from acquiring or even pursuing a nuclear weapons capability. This requirement has prevented three states from signing onto the Treaty: India, Israel, and Pakistan. (In 2003, North Korea, a former signatory, formally withdrew from the NPT.)

While the non-nuclear signatories to the NPT are prohibited from developing nuclear weapons, the nuclear weapons states are obligated to assist them in acquiring peaceful applications for nuclear technology.

In broad outline, the basic provisions of the Treaty are designed to:

  • prevent the spread of nuclear weapons (Articles I and II);
  • provide assurance, through international safeguards, that the peaceful nuclear activities of states that have not already developed nuclear weapons will not be diverted to making such weapons (Article III);
  • promote, to the maximum extent consistent with the other purposes of the Treaty, the peaceful uses of nuclear energy, including the potential benefits of any peaceful application of nuclear technology to be made available to non-nuclear parties under appropriate international observation (Articles IV and V); and
  • express the determination of the parties that the Treaty should lead to further progress in comprehensive arms control and nuclear disarmament measures (Article VI).

In accordance with the terms of the NPT, a conference was held in 1995 to decide whether the NPT should continue in force indefinitely or be extended for an additional fixed period. On May 11, 1995, more than 170 countries attending the NPT Review and Extension Conference in New York decided to extend the treaty indefinitely and without conditions.

Strategic Arms Limitation Talks/Treaty

The first series of Strategic Arms Limitation Talks (SALT) extended from November 1969 to May 1972. During that period, the United States and the Soviet Union negotiated the first agreements to place limits and restraints on some of their most important nuclear weapons systems.

At the time, American and Soviet weapons systems were far from symmetric. Further, the defense needs and commitments of the two superpowers differed considerably. The United States had obligations for the defense of allies overseas, including the nations of the North Atlantic Treaty Organization, Japan, and South Korea, while the Soviet Union’s “allies” were its near neighbors. All these circumstances made for difficulties in equating specific weapons, or categories of weapons, and in defining overall strategic equivalence.

The first round of SALT was brought to a conclusion on May 26, 1972, after two and a half years of negotiation, when President Richard Nixon and General Secretary Leonid Brezhnev signed the Anti-Ballistic Missile Treaty and the Interim Agreement on strategic offensive arms.

Anti-Ballistic Missile Treaty

In the Treaty on the Limitation of Anti-Ballistic Missile (ABM) Systems, the United States and the Soviet Union agreed that each party may have only two ABM deployment areas, restricted and located to preclude providing a nationwide ABM defense or from becoming the basis for developing one. Thus, each country agreed not to challenge the penetration capability of the other’s retaliatory nuclear missile forces.

The treaty permitted each side to have one ABM system to protect its capital and another to protect one ICBM launch area. The two sites defended had to be at least 1,300 kilometers apart to prevent the creation of any effective regional defense zone or the beginnings of a nationwide system. A 1974 protocol provided that each side could only have one site, either to protect its capital or to protect one ICBM launch area.

Precise quantitative and qualitative limits were imposed on the deployed ABM systems. Further, to decrease the pressures of technological change and corresponding unsettling effect on the strategic balance, both sides agreed to prohibit the development, testing, or deployment of sea-based, air-based, or space-based ABM systems and their components, along with mobile land-based ABM systems. Should future technology bring forth new ABM systems “based on other physical principles” than those employed in then-current systems, it was agreed that limiting such systems would be discussed in accordance with the treaty’s provisions for consultation and amendment.

In June 2002, the United States withdrew from the ABM Treaty to pursue a national ballistic missile defense program.

Interim Agreement-Strategic Arms Limitation Talks (SALT) I

As its title suggests, the Interim Agreement on Certain Measures with Respect to the Limitation of Offensive Arms was limited in duration and scope. It was intended to remain in force for only five years. Both countries agreed to continue negotiations toward a more comprehensive agreement as soon as possible. The scope and terms of any new agreement were not to be prejudiced by the provisions of the 1972 interim accord.

Thus, the Interim Agreement was intended as a holding action, which was designed to complement the ABM Treaty by limiting competition in offensive strategic arms and by providing time for further negotiations. The agreement essentially froze existing levels of strategic ballistic missile launchers (operational or under construction) for both sides. It permitted an increase in submarine launched ballistic missile (SLBM) launchers up to an agreed level for each party provided that the party dismantle or destroy a corresponding number of older ICBM or SLBM launchers.

In view of the many asymmetries between the United States and the Soviet Union, imposing equivalent limitations required complex and precise provisions. At the date of signing, the United States had 1,054 operational land-based ICBM launchers, with none under construction, and the Soviet Union had an estimated 1,618 ICBM launchers, including operational launchers and launchers under construction. Launchers under construction were permitted to be completed. Yet, neither side would be authorized to start construction of additional fixed land-based ICBM launchers during the period of the agreement, excluding the relocation of existing launchers. Launchers for light or older ICBMs could not be converted into launchers for modern heavy ICBMs. This prevented the Soviet Union from replacing older missiles with missiles such as the SS-9, which in 1972 was the largest and most powerful missile in the Soviet inventory and a source of particular concern to the United States.

Within these limitations, modernization and replacements were permitted, but in the process of modernizing, the dimensions of silo launchers could not be significantly increased. A discussion on mobile ICBMs was not included in the text of this treaty.

Strategic Arms Limitation Treaty-SALT II

In accordance with Article VII of the Interim Agreement, in which the sides committed themselves to continue active negotiations on strategic offensive arms, the SALT II negotiations began in November 1972. The primary goal of SALT II was to replace the Interim Agreement with a long-term comprehensive treaty providing broad limits on strategic offensive weapons systems. The principal U.S. objectives as the SALT II negotiations began were: to provide for equality in the aggregate numbers of strategic nuclear delivery vehicles for the two sides, to begin the process of reducing the number of these delivery vehicles, and to impose restraints on qualitative developments that could threaten future stability.

Early discussion focused on two key areas: the weapon systems to be included and factors used to determine equality in numbers of strategic nuclear delivery vehicles. Such factors accounted for the important differences between each side’s military forces, bans on new systems, qualitative limits, and a Soviet proposal to restrict U.S. forward-based systems. The two sides held widely diverging positions on many of these issues. In subsequent negotiations, the United States and the Soviet Union agreed on a general framework for SALT II.

The treaty included detailed definitions of limited systems, provisions to enhance verification, a ban on circumvention of the provisions of the agreement, and a provision outlining the duties of the Security Council in connection with SALT II. The terms of the treaty were intended to remain in force through 1985.

The completed SALT II agreement was signed by President Jimmy Carter and General Secretary Leonid Brezhnev in Vienna on June 18, 1979. President Carter transmitted it to the Senate on June 22, 1979, for ratification. United States ratification of SALT II was delayed due to the Soviet invasion of Afghanistan. Although the treaty remained unratified, each party was individually bound under international law to refrain from acts that would defeat the object and purpose of the treaty until the country had made its intentions clear not to become a party to the treaty.

SALT II never entered into force.

Threshold Test Ban Treaty

The Treaty on the Limitation of Underground Nuclear Weapon Tests, also known as the Threshold Test Ban Treaty (TTBT), was signed in July 1974. It established a nuclear “threshold” by prohibiting tests with a yield exceeding 150 kilotons (equivalent to 150,000 tons of TNT).

The TTBT included a protocol that specified the technical data to be exchanged and limited weapon testing to designated test sites to simplify verification efforts. The data to be exchanged included information on geographical boundaries and the geology of the testing areas. Geological data, including such factors as density of rock formation, water saturation, and depth of the water table, are useful in verifying test yields because the seismic signal produced by a given underground nuclear explosion varies with these factors at the test location. After an actual test had taken place, the geographic coordinates of the test location were to be furnished to the other party to help in assessing geological setting and yield.

The treaty also stipulated that data would be exchanged on a certain number of tests for calibration purposes. By establishing the correlation between the stated yield of an explosion at the specified sites and the seismic signals produced, both parties could more accurately assess the yields of explosions based primarily on the measurements derived from their seismic instruments.

Although the TTBT was signed in 1974, it was not sent to the U.S. Senate for ratification until July 1976. Submission was held in abeyance until the companion Treaty on Underground Nuclear Explosions for Peaceful Purposes (or the Peaceful Nuclear Explosions Treaty (PNET)) had been successfully negotiated in accordance with Article III of the TTBT.

Neither the United States nor the Soviet Union ratified the TTBT or the PNET until 1990. However, in 1976 each party separately announced its intention to observe the Treaty limit of 150 kilotons, pending ratification.

The United States and the Soviet Union began negotiations in November 1987 to reach an agreement on additional verification provisions that would make it possible for the United States to ratify the two treaties. In 1990, the parties reached an agreement on additional verification provisions; these provisions were introduced in new protocols substituting for the original protocols. The TTBT and PNET both entered into force on December 11, 1990.

Peaceful Nuclear Explosions Treaty

In preparing the TTBT, the United States and the Soviet Union recognized the need to establish an appropriate agreement to govern underground nuclear explosions for peaceful purposes.

In the Treaty on Underground Nuclear Explosions for Peaceful Purposes, the United States and the Soviet Union agreed not to carry out:

  • any individual nuclear explosions with a yield exceeding 150 kilotons;
  • any group explosion (consisting of a number of individual explosions) with an aggregate yield exceeding 1,500 kilotons; and
  • any group explosion with an aggregate yield exceeding 150 kilotons unless the individual explosions in the group could be identified and measured by agreed verification procedures.

The parties reserved the right to carry out nuclear explosions for peaceful purposes in the territory of another country if requested to do so, but only in full compliance with the yield limitations and other provisions of the PNET and in accordance with the NPT.

The Protocol to the PNET sets forth the specific agreed arrangements for ensuring that no weapons-related benefits precluded by the TTBT are derived by carrying out a nuclear explosion used for peaceful purposes.

The agreed statement that accompanies the Peaceful Nuclear Explosions Treaty specifies that a “peaceful application” of an underground nuclear explosion would not include the developmental testing of any nuclear explosive. Nuclear explosive testing must be carried out at the nuclear weapon test sites specified by the terms of the TTBT and would be treated as the testing of a nuclear weapon.

The provisions of the PNET, together with those of the TTBT, establish a comprehensive system of regulations to govern all underground nuclear explosions of the United States and the Soviet Union. The interrelationship of the TTBT and the PNET is further demonstrated by the provision that neither party may withdraw from the PNET while the TTBT remains in force. Conversely, either party may withdraw from the PNET upon termination of the TTBT.

Intermediate-Range Nuclear Forces Treaty

The Treaty between the United States of America and the Union of Soviet Socialist Republics on the Elimination of their Intermediate-Range and Shorter-Range Missiles, commonly referred to as the Intermediate-Range Nuclear Forces (INF) Treaty, was signed by President Ronald Reagan and General Secretary Mikhail Gorbachev on December 8, 1987, at a summit meeting in Washington, D.C. The INF Treaty required the destruction of ground-launched ballistic and cruise missiles with ranges between 500 and 5,500 kilometers, their launchers, and their associated support structures and support equipment within three years following the treaty’s entry into force. It also established a verification regime to help ensure compliance with the total ban on possession and use of these missiles. At the time of its signature, the treaty’s verification regime was the most detailed and stringent in the history of nuclear arms control.

The treaty entered into force upon the exchange of instruments of ratification in Moscow on June 1, 1988. In late April and early May 1991, the United States eliminated its last ground-launched cruise missile and ground-launched ballistic missile covered under the INF Treaty. The last declared Soviet SS-20 was eliminated on May 11, 1991. In total, 2,692 missiles were eliminated after the treaty’s entry into force.

Following the December 25, 1991, dissolution of the Soviet Union, the United States informed 12 former Soviet Republics that it held them accountable as successor states under the INF Treaty; however, some of these states never agreed. Six of these 12 former Soviet Republics had facilities subject to inspection on their territory, namely Russia, Ukraine, Belarus, Kazakhstan, Turkmenistan, and Uzbekistan. Converting what was previously a bilateral U.S.-Soviet INF Treaty to a multilateral treaty required establishing agreements between the United States and the relevant Soviet successor states on numerous issues. Among the tasks undertaken were: the settlement of costs connected with implementation of the new, multilateral treaty; the establishment of new points of entry in Belarus, Kazakhstan, and Ukraine through which to conduct inspections of the former INF Treaty facilities in those countries; and the establishment of communications links between the United States and those countries for the transmission of various treaty-related notifications.

In a joint statement to the United Nations General Assembly in 2007, the United States and the Russian Federation called on all countries to join a global INF Treaty. The leadership of the Russian Federation cited concerns that, without other countries joining the treaty, it would no longer prove useful. Since that time both the Obama and Trump administrations, as well as NATO leaders, have stated Russia was in breach of the treaty. Specifically, the concern was the Russian SSC-8 ground-launched cruise missile violated the treaty. Russia has denied these accusations.

As a result, on December 4, 2018, the United States announced that the Russian Federation was in material breach of the INF Treaty and that unless Russia returned to full and verifiable compliance in 60 days, the U.S. would suspend its obligations under the treaty as a consequence for Russia’s material breach. On February 2, 2019, the United States suspended its obligations under the INF Treaty and provided Russia and other treaty Parties with formal notice that the United States would withdraw from the INF Treaty in six months, pursuant to Article XV of the treaty. On May 4, 2019, President Putin signed an executive order suspending Russia’s compliance with the INF Treaty and on July 3, 2019, signed into law Russia’s suspension of its obligations under the INF Treaty. The United States officially withdrew from the treaty on August 2, 2019.

Strategic Arms Reduction Talks (START) Treaty

After nine years of negotiations, the Treaty on the Reduction and Limitation of Strategic Offensive Arms, or START Treaty, was signed in Moscow on July 31, 1991. Five months later, the Soviet Union dissolved, and four independent states with strategic nuclear weapons on their territories came into existence: Belarus, Kazakhstan, Russia, and Ukraine.

Through the Lisbon Protocol to the START Treaty, signed on May 23, 1992, Belarus, Kazakhstan, Russia, and Ukraine became parties to the treaty as legal successors to the Soviet Union. In December 1994, the parties to START I exchanged instruments of ratification and the START Treaty entered into force. In parallel with the Lisbon Protocol, the three non-Russian states agreed to send all nuclear weapons back to the Russian Federation and join the NPT as non-nuclear weapons states.

The Treaty required reductions in strategic offensive arms to equal aggregate levels, from a high of some 10,500 in each arsenal. The central limits include:

  • 1,600 strategic nuclear delivery vehicles;
  • 6,000 accountable warheads;
  • 4,900 ballistic missile warheads;
  • 1,540 warheads on 154 heavy ICBMs; and
  • 1,100 warheads on mobile ICBMs.

While the Treaty called for these reductions to be carried out over seven years, in practice, all the Lisbon Protocol signatories began deactivating and eliminating systems covered by the agreement prior to its entry into force. START I was negotiated with effective verification in mind. The basic structure of the Treaty was designed to facilitate verification by national technical means (NTM),2 and the Treaty contains detailed, mutually reinforcing verification provisions to supplement NTM.

On December 5, 2001, the United States and Russia announced that they had met the final START Treaty limits. This completed the largest arms control reductions in history.

The START Treaty was intended to be a 15-year commitment with the option to extend it in 5-year increments. However, the United States and the Russian Federation allowed the treaty to expire on December 5, 2009. By that time, negotiations for a new START Treaty were ongoing, and the agreement, called New START, was signed in Prague on April 8, 2010.

1991 Presidential Nuclear Initiatives

On September 27, 1991, President George H.W. Bush announced that the United States would eliminate its entire worldwide inventory of ground-launched tactical nuclear weapons and would remove tactical nuclear weapons from all U.S. Navy surface ships, attack submarines, and land-based naval aircraft bases during normal circumstances. In addition, President Bush declared that U.S. strategic bombers would be taken off alert and that ICBMs scheduled for deactivation under the START Treaty would also be taken off alert. These unilateral arms reductions are known as the 1991 Presidential Nuclear Initiatives.

On October 5, 1991, about one week after President Bush announced the U.S. initiatives, Soviet President Mikhail Gorbachev pledged to destroy all nuclear artillery ammunition and nuclear mines, to remove nuclear warheads from anti-aircraft missiles and all theater nuclear weapons on surface ships and multi-purpose submarines, to de-alert strategic bombers, and to abandon plans of developing a small mobile ICBM and not to increase or modernize mobile ICBMs. He also pledged to reduce an additional 1,000 nuclear warheads beyond the reductions required by the START Treaty and stated that the country would observe a one-year moratorium on nuclear weapons testing. In January 1992, Russian President Boris Yeltsin asserted Russia’s status as a legal successor to the Soviet Union in international obligations. President Yeltsin also made several pledges to reduce Russian nuclear capabilities.

Treaty on Open Skies

The Treaty on Open Skies was signed in Helsinki, Finland, on March 24, 1992, and entered into force on January 1, 2002. The Eisenhower Administration originally proposed the notion of an Open Skies regime in 1955, but the proposal was rejected by the Soviet Union. The Open Skies concept was revisited in 1989, and in February 1990, members of NATO and the Warsaw Pact began negotiations to establish an Open Skies regime. Additional negotiations in Vienna, Austria, included observers from the Organization for Security and Cooperation in Europe, and concluded in 1992 with the signing of the Treaty on Open Skies. The treaty currently includes 34 State Parties (Kyrgyzstan has signed, but not ratified) and is unlimited in duration.

The treaty aims to promote openness and transparency of military forces and activities among its State Parties. Additionally, it provides further means of verifying states’ compliance with other arms control agreements. It establishes a regime of observation flights over its signatories’ territories with unarmed, fixed-wing aircraft that must be equipped with specific types of sensors and camera resolution. Each State Party is allocated a certain number of observation flights it may conduct and a certain number of observation flights it must accept over its own territory. The allocated observation flights are referred to as “quotas,” which are reviewed annually. State Parties are also able to conduct shared missions with each other, which fosters collaboration and relationships among the member states. In accordance with the treaty, all State Parties receive advanced notification of any observation flight and mission status. Additionally, any member may purchase the data collected from these observation missions.

The Open Skies Consultative Commission (OSCC) is the treaty’s implementing body and meets monthly in Vienna, Austria. The Commission is charged with responding to technical, procedural, and financial issues as well as resolving any issues related to treaty implementation and compliance. The United States formally withdrew from the treaty on November 22, 2020.


Negotiations to achieve a follow-on to the START Treaty began in June 1992. The United States and Russia agreed on the text of a Joint Understanding on the Elimination of MIRVed ICBMS and Further Reductions in Strategic Offensive Arms. The Joint Understanding called for both sides to promptly conclude a new treaty that would further reduce strategic offensive arms by eliminating all ICBMs containing Multiple Independently-Targetable Reentry Vehicles (MIRVs), including all heavy ICBMs, limiting the number of SLBM warheads to no more than 1,750, and reducing the total number of accountable warheads for each side to between 3,000 and 3,500.

On January 3, 1993, President George H.W. Bush and President Boris Yeltsin signed the Treaty between the United States of America and the Russian Federation on Further Reduction and Limitation of Strategic Offensive Arms. The treaty, often called START II, codifies the Joint Understanding signed by the two Presidents at the Washington Summit on June 17, 1992.

The 1993 START II never entered into force because of the long delay in Russian ratification and because Russia conditioned its ratification of START II on preservation of the ABM Treaty.

Comprehensive Nuclear-Test-Ban Treaty

The Comprehensive Nuclear-Test-Ban Treaty (CTBT) was negotiated at the Geneva Conference on Disarmament between January 1994 and August 1996. The United Nations General Assembly voted on September 10, 1996, to adopt the treaty by a vote of 158 in favor, three opposed, and five abstentions. President Bill Clinton was the first world leader to sign the CTBT on September 24, 1996. The CTBT bans any nuclear weapon test explosion or any other nuclear explosion. The CTBT is of unlimited duration. Each State Party has the right to withdraw from the CTBT under the standard “supreme national interest” clause. President Clinton submitted the treaty to the U.S. Senate for ratification in 1999, but the Senate failed to ratify the treaty by a vote of 51 to 48.

The treaty will enter into force following ratification by the United States and 43 other countries listed in Annex 2 of the treaty. These “Annex 2 States” are states that participated in CTBT negotiations between 1994 and 1996 and possessed nuclear power reactors or research reactors during that time. Eight of the Annex 2 States have not yet ratified the treaty, to include the United States. Therefore, the treaty has not entered into force. Nevertheless, the United States has observed a self-imposed moratorium on underground nuclear explosive testing since 1992.

Strategic Offensive Reductions Treaty

On May 24, 2002, President George W. Bush and Russian President Vladimir Putin signed the Moscow Treaty on Strategic Offensive Reductions, also called SORT or the Moscow Treaty. Under the terms of this treaty, the United States and Russia pledged to reduce their operationally deployed strategic nuclear warheads to a level between 1,700 and 2,200 by December 31, 2012, nearly two- thirds below levels at the time it was signed. Each side was to determine for itself the composition and structure of its strategic forces consistent with this limit.

Both the United States and Russia pledged to reduce their strategic offensive forces to the lowest possible levels consistent with their national security requirements and alliance obligations. The United States considered operationally deployed strategic nuclear warheads to be: reentry vehicles on ICBMs in their launchers, reentry vehicles on SLBMs in their launchers onboard submarines, and nuclear armaments loaded on heavy bombers or stored in weapon storage areas at heavy bomber bases.

The Moscow Treaty entered into force on June 1, 2003. When the New START Treaty entered into force on February 5, 2011, the Moscow Treaty was terminated.

New START Treaty

Negotiations for a new follow-on agreement to the START Treaty began in May 2009. A Joint Understanding for a Follow-on Agreement to the START Treaty was signed by the Presidents of the United States and Russia in Moscow on July 6, 2009. The successor Treaty on Measures for the Further Reduction and Limitation of Strategic Offensive Arms, known as the New START Treaty, was signed by President Barack Obama and President Dmitry Medvedev in Prague, Czech Republic, on April 8, 2010.

Under the New START Treaty, the United States and Russia agreed to significantly reduce strategic arms within seven years from February 5, 2011, the date the treaty entered into force. According to the treaty, each party has the flexibility to determine the structure of its strategic forces within the aggregate limits of the treaty. The aggregate limits set by the treaty are:

  • 1,550 deployed warheads. Warheads on deployed ICBMs and deployed SLBMs count toward this limit and each deployed heavy bomber equipped for nuclear armaments counts as one warhead toward this limit;
  • a combined limit of 800 deployed and non-deployed ICBM launchers, SLBM launchers, and heavy bombers equipped for nuclear armaments; and
  • a separate limit of 700 deployed ICBMs, deployed SLBMs, and deployed heavy bombers equipped for nuclear armaments.

The treaty has a verification regime that includes some elements of the START Treaty with new elements tailored to the limitations of the New START Treaty. Measures under the treaty include on-site inspections and exhibitions, data exchanges and notifications related to strategic offensive arms and facilities covered by the treaty, and provisions to facilitate the use of national technical means for treaty monitoring. The treaty also provides for the exchange of telemetry to increase confidence and transparency.

On February 3, 2021, the United States extended the New START Treaty with the Russian Federation for five years.

Nuclear Materials, Treaty Monitoring and Verification Technologies

To ensure confidence in the treaty regimes, a vast array of technical and non-technical verification technologies and procedures are utilized to guard against illicit nuclear activities. There are two main types of verification procedures: those designed to uncover and inhibit nuclear weapons development and/or nuclear weapons testing; and those designed to account for and monitor reductions in existing nuclear stockpiles. There are some technologies and procedures that apply to both counterproliferation activities and stockpile monitoring activities.

The Joint Comprehensive Plan of Action (JCPOA)

The Joint Comprehensive Plan of Action (JCPOA), known as the Iran nuclear deal, is an agreement on the Iranian nuclear program reached in Vienna on July 14, 2015, between Iran, the five permanent members of the United Nations Security Council-China, France, Russia, United Kingdom, United States-plus Germany (the P5+1), and the European Union.

Under JCPOA, Iran agreed to eliminate its stockpile of medium-enriched uranium, cut its stockpile of low-enriched uranium by 98%, and reduce by about two-thirds the number of its gas centrifuges for 13 years. For the next 15 years, Iran would only enrich uranium up to 3.67%. Iran also agreed not to build any new heavy-water facilities for the same period of time. Uranium enrichment activities would be limited to a single facility using first-generation centrifuges for ten years. The International Atomic Energy Agency (IAEA) would monitor and verify compliance at Iran’s nuclear facilities. In return for verifiably abiding by its commitments, Iran would receive relief from United States, European Union, and United Nations Security Council nuclear-related sanctions.

Citing issues with JCPOA, on October 13, 2017, President Donald Trump announced that the United States would not make the certification provided for under U.S. domestic law, but stopped short of terminating the agreement. Then, on April 30, 2018, the United States and Israel stated that Iran had not disclosed a past covert nuclear weapons program to the IAEA, which was required in JCPOA.

On May 8, 2018, President Trump announced the U.S. withdrawal from JCPOA, stating it failed to protect America’s national security interests. Subsequently, the United States re-imposed sanctions targeted at critical sectors of Iran’s economy, such as its energy, petrochemical, and financial sectors. On Feb. 18, 2021, the newly inaugurated Biden Administration formally rescinded Trump’s request that all sanctions lifted in accordance with the JCPOA be reimposed.

Convention on Physical Protection of Nuclear Materials (CPPNM) and its 2005 Amendment

Recognizing the need for international cooperation in protecting nuclear material used for peaceful purposes, the IAEA established the legal framework for physical protection of such materials on March 3, 1980. The treaty was entered into force in 1987 with an additional amendment in 2005.

The treaty acknowledges the potential benefits of nuclear energy for peaceful purposes and the need to avert all unlawful pursuits of such material including the seizing, trafficking, or sabotaging of such materials. The treaty only protects nuclear material in international transport and does not entail such materials used for military purposes.

The basic obligations of the treaty are:

  • each State Party shall not export, import, or authorize the export of nuclear material unless the State Party has received assurances that these materials will be protected during international transport in accordance with the levels of protection determined by the Convention;
  • co-operate with the other treaty members in the recovery and storing of stolen nuclear materials, including the sharing of information on such stolen materials;
  • criminalize misuse of nuclear materials, including threatening to misuse nuclear materials; and
  • follow the standards set by the treaty in the physical protection of nuclear materials in international transport.

Whereas the original treaty focused on the protection of international transport of nuclear materials, the 2005 amendment expanded the treaty’s legal framework into requiring States to protect their domestic nuclear materials. This domestic protection includes the use, storage, and transport of nuclear materials.

Counterproliferation Verification Technologies

Counterproliferation verification technologies are most commonly employed to support and ensure confidence in nuclear weapons treaties affecting non- nuclear weapons states and/or those states not in compliance with either the NPT or IAEA safeguards. These activities include: intrusive, short-notice inspections by the IAEA; a declaration of nuclear materials; satellite surveillance of suspected nuclear facilities; and, in the event of a confirmed or suspected nuclear detonation, international seismic monitoring, air and materials sampling, hydroacoustic and infrasound monitoring, and space-based nuclear energy detection resources.

Inspections of nuclear or suspected nuclear facilities as well as reporting requirements are generally administered by the IAEA, under the auspices of the NPT and the Additional Protocols. During these inspections, trained IAEA inspectors collect environmental samples to scan for illicit nuclear substances, verify facility design information, and review the country’s nuclear fuel cycle processes. Remote inspection activities can also be used to monitor movements of declared material in a facility and to evaluate information derived from a country’s official declarations and open source information.

Satellite surveillance of suspected nuclear facilities is generally not proscribed by nonproliferation treaties and agreements with non-nuclear weapons states, but it is employed by domestic intelligence collection programs and can aid in counterproliferation verification. These activities, for instance, can remotely monitor and verify either the destruction or expansion of existing nuclear facilities.

International seismic monitoring is conducted by both the international community, through a network of CTBT Organization (CTBTO) monitoring stations, and the United States, through an independent network of monitoring stations. Both systems rely on strategically placed seismic monitors to detect nuclear detonations on or below the Earth’s surface.

Air and materials sampling and hydroacoustic and infrasound monitoring are also recognized verification technologies that could be used to detect and/or confirm a nuclear detonation. Nuclear events produce very specific, and generally easily recognizable, post-detonation characteristics, to include the dispersal of radioactive fallout, atmospheric pressure waves, and infrared radiation. These sampling and monitoring activities are generally considered to be national technical nuclear forensics activities. (For more information on national technical nuclear forensics, see Chapter 11: Nuclear Threat Reduction.)

Lastly, space-based nuclear energy sensors are particularly adept at detecting surface and above surface nuclear detonations. These satellites use X-ray, neutron, electromagnetic pulse (EMP) and gamma-ray detectors as well as detectors capable of distinguishing the characteristic “double flash” of a nuclear burst. Sub-surface bursts, however, would go largely undetected by this set of technologies.

Stockpile Monitoring

Stockpile monitoring includes those activities designed to ensure compliance with nuclear weapons reductions or stockpile surveillance, for example, the NPT (as it relates to declared and allowed nuclear weapons states) and New START. These activities include bilateral on-site inspections, unique identifiers for nuclear warheads, national technical means, data exchange and notifications, and telemetric information from intercontinental and submarine-launched ballistic missile (ICBM and SLBM) launches. These procedures are designed to balance the sovereignty and security interests of each participating nation against denuclearization goals.

Bilateral on-site inspections are conducted under the auspices of bilateral treaty organizations, which stipulate the number and type of inspections. For the United States, the only major nuclear treaty that allows for bilateral inspections is New START. New START allows for two different types of inspections, with a total of 18 possible inspections each year. The first type focuses on sites with deployed and non-deployed strategic systems; whereas the second focuses on sites with only non-deployed (or converted non-nuclear) strategic systems. During the inspections, inspectors are allowed to confirm the number of reentry vehicles on deployed ICBMs and SLBMs, numbers related to non-deployed launcher limits, weapons system conversions or eliminations, and facility eliminations. To aid in the inspection process, unique identifiers are assigned to each nuclear delivery vehicle (i.e., ICBMs, SLBMs, and heavy bombers). These are confirmed against data exchange and notification figures, which list the numbers, location, and technical characteristics of delivery vehicles and facilities.

Nuclear Security Summits

In April 2010, in response to U.S. prompting for a new international effort to secure vulnerable nuclear material around the world, the first Nuclear Security Summit on nuclear terrorism was hosted by the United States. Four Nuclear Security Summits were convened with a total of four international organizations and 53 countries, including the P5 nations (nuclear weapons states) and states not party to the NPT. The Summits were held on the following dates:

  • April 12–13, 2010, Washington, D.C., United States
  • March 26–27, 2012, Seoul, South Korea
  • March 24–25, 2014, The Hague, Netherlands
  • March 31–April 1, 2016, Washington, D.C., United States

The summit series addressed cooperative measures necessary for the international community to combat the threat of nuclear terrorism, protect nuclear materials and facilities, and prevent illicit trafficking of nuclear weapons. Each summit addressed key nuclear security issues with the understanding that the threat of nuclear terrorism cannot be undertaken by any individual nation but must be confronted by the international community writ large.

1 On January 30, 1992, the Russian Embassy in the United States informed the State Department that the Russian Federation would continue to exercise the rights and fulfill the obligations arising from the Treaty as a nuclear-weapon state.

2 National technical means of verification are monitoring techniques, such as satellite photography, used to verify adherence to treaties.