The Nuclear Non-Proliferation Regime

On 5 August 1963, the United States, the Soviet Union, and the United Kingdom signed the Partial Test Ban Treaty in Moscow, prohibiting nuclear explosions in the atmosphere, in outer space, and underwater. The agreement followed the Cuban Missile Crisis of October 1962 and years of public alarm over radioactive fallout from atmospheric testing. It did not ban underground testing, which the parties could not yet verify, but it ended the most dangerous form of nuclear testing and established a pattern of negotiated arms control. France and China, which had not joined, continued atmospheric tests for years. The treaty demonstrated that even intense rivals could constrain the arms race through mutual verification and diplomacy, setting the stage for broader non-proliferation efforts.

Location: Moscow, Soviet Union

On 14 February 1967, Latin American and Caribbean states signed the Treaty of Tlatelolco in Mexico City, creating the world's first populated nuclear-weapon-free zone. The treaty obliged its parties not to acquire or test nuclear weapons on their territory and established the Agency for the Prohibition of Nuclear Weapons in Latin America and the Caribbean to verify compliance. It came in the aftermath of the Cuban Missile Crisis, which had brought the region to the brink of nuclear war, and reflected the determination of Latin American states to keep such weapons out of their hemisphere. The treaty also established that nuclear-weapon states could sign protocols committing them to respect the zone's status. Tlatelolco proved that regional approaches could complement global non-proliferation efforts and inspired later free-zone treaties in other parts of the world.

Location: Mexico City, Mexico

On 1 July 1968, the Treaty on the Non-Proliferation of Nuclear Weapons was opened for signature at the United Nations in New York, with the United States, the Soviet Union, and the United Kingdom among the first signatories along with dozens of other states. The treaty's structure reflected a hard-won bargain: the five recognized nuclear-weapon states would not transfer weapons or assist others in acquiring them, non-nuclear-weapon states would not acquire them, and all parties would have access to peaceful nuclear technology under safeguards administered by the International Atomic Energy Agency. The treaty also committed the nuclear-weapon states to pursue negotiations in good faith toward nuclear disarmament, a provision that would prove central to later disputes. France and China, which had not yet signed, stayed outside the treaty for years. The NPT codified the nuclear hierarchy of the mid-1960s into international law, an arrangement that remains controversial among many non-nuclear states.

Location: New York, USA

On 5 March 1970, the NPT entered into force after sufficient ratifications had been deposited, including those of the three nuclear-weapon states that had signed. The treaty established the IAEA safeguards system as the mechanism for verifying that non-nuclear-weapon states were not diverting nuclear material to weapons programs. From the beginning, the treaty's durability depended on the credibility of the disarmament pledge, and many non-nuclear states entered the regime with reservations about a permanent nuclear hierarchy. Over the following decades, the NPT would grow to include nearly all the world's states, becoming the most widely adhered-to arms-control treaty in existence. Its entry into force marked the moment when the principle of nuclear non-proliferation became a binding international obligation rather than a political aspiration.

Location: New York, USA

On 18 May 1974, India detonated a nuclear device at the Pokhran test range in Rajasthan, in an operation code-named Smiling Buddha. The test made India the first state outside the treaty's recognized nuclear-weapon states to demonstrate a nuclear explosive capability. India, which had not signed the NPT, described the test as a peaceful nuclear explosion, but the distinction did little to change its strategic implications. The test alarmed Pakistan and other neighbors, accelerated nuclear research and procurement across South Asia, and intensified debate within the international community about the fairness of the NPT's nuclear hierarchy. It also spurred efforts to strengthen safeguards, including the creation of the Nuclear Suppliers Group to control nuclear exports.

Location: Pokhran, India

On 12 December 1985, North Korea acceded to the NPT, becoming a non-nuclear-weapon state party under the treaty. The accession followed years of pressure from the Soviet Union, which was North Korea's principal supplier of nuclear technology, and from other states concerned about Pyongyang's nuclear ambitions. Under the treaty, North Korea was required to conclude a safeguards agreement with the IAEA within eighteen months, but implementation was delayed for years. The country's eventual compliance questions, including discrepancies in its declared nuclear material, would become the focus of international attention in the 1990s. North Korea's accession proved to be a temporary commitment rather than a permanent one, setting the stage for its later withdrawal and nuclear program.

Location: Pyongyang, North Korea

On 11 May 1995, the Review and Extension Conference of the NPT voted to extend the treaty indefinitely, rather than for a fixed further period. The original treaty had been set for a twenty-five-year term, creating a deadline that forced a comprehensive review of its bargain. Many non-nuclear states, particularly in the Non-Aligned Movement, argued that indefinite extension would remove the leverage the treaty's expiry gave them in pressing the nuclear-weapon states on disarmament. The nuclear-weapon states, supported by a broad coalition, secured the indefinite extension through a combination of persuasion and concessions, including commitments to strengthen the review process and pursue a comprehensive test-ban treaty. The decision made the NPT a permanent feature of international law, but it also entrenched the grievances of states that felt the disarmament promise had been neglected.

Location: New York, USA

On 28 May 1998, Pakistan conducted a series of nuclear tests at Chagai in Balochistan, responding to India's tests at Pokhran two weeks earlier, on 11 and 13 May 1998. Both countries, which had never signed the NPT, thereby openly demonstrated their nuclear capabilities and declared themselves nuclear powers. The tests triggered international sanctions and condemnation but did not reverse either program, and they transformed South Asia into an openly nuclear-armed region. The tests underscored the limits of the NPT regime, which could not bind states that had remained outside the treaty. They also confirmed a pattern in which technological capability and regional rivalry, rather than treaty commitments, ultimately determined nuclear proliferation.

Location: Chagai, Pakistan

On 10 January 2003, North Korea announced its withdrawal from the NPT, becoming the first and only state to leave the treaty. The announcement followed years of confrontation over its nuclear program, the suspension of a 1994 agreement with the United States, and the revelation of a covert uranium enrichment effort. North Korea invoked its right to withdraw under Article X of the treaty, citing what it described as threats to its security. In the following years, North Korea developed nuclear weapons and conducted a series of tests beginning in 2006, openly defying the regime it had once joined. Its withdrawal exposed a structural weakness of the NPT: the treaty's exit clause, designed as a sovereign right, had been used by a state to escape the regime and pursue the very capability the treaty was meant to prevent.

Location: Pyongyang, North Korea

On 22 January 2021, the Treaty on the Prohibition of Nuclear Weapons (TPNW) entered into force, ninety days after the fiftieth state ratified it. Adopted by the United Nations General Assembly on 7 July 2017, the treaty bans the development, testing, production, acquisition, stockpiling, and use of nuclear weapons, and obliges parties not to assist in such activities. The TPNW emerged from the humanitarian initiative, a coalition of states and civil society groups who argued that the NPT's gradualist approach to disarmament had failed to deliver meaningful progress. None of the nuclear-armed states and no state under extended nuclear deterrence arrangements has joined the treaty. Its entry into force has sharpened the divide within the non-proliferation community, between states committed to an immediate legal ban and those that regard deterrence as necessary, while adding a new pressure point to the debate over the NPT's future.

Location: New York, USA