Major Nuclear Arms Control Treaties and Agreements

Nuclear arms control agreements seek to prevent the spread of nuclear weapons, limit arsenals and restrict testing. They combine legal obligations with verification and transparency measures, but differ in membership, scope and current status.

The Non-Proliferation Treaty (NPT)

The Treaty on the Non-Proliferation of Nuclear Weapons opened for signature in 1968 and entered into force in 1970. It rests on three linked objectives: preventing nuclear proliferation, pursuing disarmament and facilitating peaceful uses of nuclear energy.

• Nuclear-weapon states: The treaty recognises China, France, Russia, the United Kingdom and the United States as nuclear-weapon states (NWS), defined as states that detonated a nuclear device before 1 January 1967.
• Core obligations: Non-nuclear-weapon states (NNWS) parties undertake not to acquire nuclear weapons. NWS parties undertake not to transfer them and to pursue nuclear disarmament in good faith.
• Peaceful uses and verification: Parties agree to facilitate cooperation in peaceful nuclear energy. The International Atomic Energy Agency (IAEA) verifies NNWS compliance with safeguards obligations.

NPT Review Conferences are held every five years to assess the treaty’s operation. NATO Allies continue to express commitment to the NPT and its objectives, including the verifiable elimination of nuclear weapons. In October 2026, the UN First Committee approved a draft resolution concerning the Twelfth NPT Review Conference.

New START and Strategic Arms Limits

The New Strategic Arms Reduction Treaty (New START) was the last bilateral treaty limiting the strategic nuclear arsenals of the United States and Russia. It entered into force on 5 February 2011 and was extended for five years in 2021.

• Numerical limits: Each side was limited to 1,550 deployed strategic warheads, 700 deployed ICBMs, submarine-launched ballistic missiles (SLBMs) and heavy bombers, and 800 deployed and non-deployed launchers.
• Suspension: Russia suspended its participation on 21 February 2023 but stated it would continue observing the treaty’s numerical limits.
• Expiry: New START expired on 5 February 2026. Russia had proposed in September 2025 to observe the limits for a further year, provided the United States reciprocated; the United States did not formally respond.

Its expiry leaves the two countries without a legally binding agreement to limit their strategic arsenals and provide transparency over them. The loss of such arrangements is significant for arms control because limits and information-sharing can help reduce uncertainty between nuclear-armed states.

Comprehensive Nuclear-Test-Ban Treaty (CTBT)

The CTBT prohibits all nuclear weapon test explosions and other nuclear explosions, whether for military or civilian purposes and in any environment. The UN General Assembly adopted it on 10 September 1996; it opened for signature on 24 September 1996. It has not entered into force.

• Status: As of July 2026, 188 states had signed and 179 had ratified the treaty.
• Entry-into-force requirement: Ratification by all 44 designated Annex 2 states is required. Nine remain outstanding: China, Egypt, India, Iran, Israel, North Korea, Pakistan, Russia and the United States.
• Ratification positions: Russia ratified the treaty in 2000 but withdrew its ratification in 2023. The United States has signed but not ratified it.
• Testing and diplomacy: A de facto global nuclear test moratorium is largely observed. North Korea is the only country confirmed to have conducted nuclear explosive tests this century. On 27 October 2026, the UN First Committee approved a resolution stressing the urgency of the treaty’s entry into force.

INF and Open Skies Treaties

The Intermediate-Range Nuclear Forces (INF) Treaty and the Treaty on Open Skies addressed different elements of security: the former eliminated a class of missiles, while the latter enabled aerial observation to support transparency.

• INF Treaty: Signed by the United States and the Soviet Union on 8 December 1987, it entered into force on 1 June 1988. It required the elimination of ground-launched ballistic and cruise missiles with ranges of 500–5,500 kilometres.
• INF withdrawal: The United States withdrew on 2 August 2019, citing Russian non-compliance. Russia formally suspended the treaty the next day, effectively ending the agreement.
• Open Skies: In force from 1 January 2002, the treaty allowed unarmed observation flights over the territories of member states to promote transparency about military forces and activities.
• Open Skies withdrawals: The United States withdrew in November 2020, citing alleged Russian violations. Russia announced its intention to withdraw in January 2021 and completed its withdrawal in December 2021, diminishing the treaty’s strategic value.

Treaty on the Prohibition of Nuclear Weapons (TPNW)

The TPNW prohibits the development, testing, production, manufacture, acquisition, possession and stockpiling of nuclear weapons. It also prohibits their use or threat of use, as well as assistance with prohibited activities. The treaty entered into force on 22 January 2021. As of 29 October 2026, 75 states were parties and 26 were signatories. No nuclear-armed state has joined. The TPNW’s comprehensive prohibition and the NPT’s broader participation and verification framework reflect distinct approaches within multilateral diplomacy. Together with limits and testing restrictions, they illustrate how non-proliferation and disarmament efforts depend on both agreed rules and state participation.

Key Prelims Takeaways

• NPT: Entered into force in 1970; recognises five NWS and covers non-proliferation, disarmament and peaceful nuclear cooperation.
• New START: Limited US–Russia strategic arsenals; expired on 5 February 2026.
• CTBT: Adopted in 1996; not in force and requires ratification by all 44 Annex 2 states.
• INF Treaty: Eliminated US–Soviet/Russian ground-launched missiles with ranges of 500–5,500 kilometres; ended in 2019.
• Open Skies: Enabled unarmed observation flights; the United States and Russia withdrew by December 2021.
• TPNW: Entered into force in 2021; no nuclear-armed state has joined.

Recent Context

On 28 October 2026, Russia’s Ministry of Defence said it successfully test-fired a Bulava missile from the submerged submarine Generalissimo Suvorov in the Sea of Okhotsk, describing the launch as routine combat training. The claims were not independently verified by international media; Russia presented the launch as demonstrating second-strike capability.