This year marks the 55th anniversary of the treaty institutionalizing the first nuclear-weapon-free zone (NWFZ) in a densely populated area. The Treaty for the Prohibition of Nuclear Weapons in Latin America and the Caribbean, commonly known as the Treaty of Tlatelolco, opened for signatures on February 14, 1967. It entered into force on April 22, 1968. The Treaty of Tlatelolco became a call to control nuclear dangers after the world was on the brink of nuclear war in 1962. The treaty also became a blueprint that other regions followed in attempts to at least create regional limits on nuclear weapons. In this text, I explain the importance of the Treaty of Tlatelolco and why the Latin American nuclear-weapon-free zone is an essential nuclear arms control mechanism. Tlatelolco was an instrument to promote stability The Cuban missile crisis in October 1962 made Latin American governments very worried about a potential nuclear arms race in their vicinity between the Cold War superpowers. The unveiled risk of a nuclear war in the Caribbean made Latin American governments aware of the need to design limits on nuclear arsenals through multilateral agreements and institutions. A consensus emerged around building a regional nuclear arms control mechanism to reduce the likelihood of a nuclear war in Latin America, or at least to make it less catastrophic if it should occur. In less than five years, Latin American governments crafted a treaty constituting the first NWFZ in a densely populated area to prevent nuclear dangers. Five years sounds like a long time, but it was swift if we consider how slow international negotiations around nuclear security issues can go. Moreover, the regime changes happening in Latin America in those years complicated matters even more. For example, Brazilian authorities were some of the first actors to propose denuclearizing Latin America. In January 1962, Brazil and Mexico suggested prohibiting nuclear arsenals in the region. A couple of years later, a military coup ousted the democratic leaders in Brazil and institutionalized a dictatorship that did not want to renounce the option of using nuclear technology for military purposes in case it became necessary. Brazil was not the only country with a democratic breakdown in the mid-1960s. The spread of authoritarian governments in Latin America modified preferences around denuclearization and complicated arms control negotiations. Despite political and regime changes in various countries in the region, the Treaty of Tlatelolco opened for signatures. The treaty institutionalized restraints for non-nuclear-weapon states and commitments from nuclear powers. Different regions have used the Latin American NWFZ as an example of controlling nuclear dangers. In the following two sections, I delve into two reasons why the Treaty of Tlatelolco became an example that other states imitated. Two explanations behind Tlatelolco’s appeal The possibility of nuclear destruction produced anxieties that nuclear and non-nuclear powers alike shared. The United States and the Soviet Union welcomed the Latin American non-proliferation efforts. With the Treaty of Tlatelolco, Latin American states renounced their prerogatives to build, acquire, and store nuclear weapons. The treaty was not just an agreement among countries without nuclear arsenals. Nuclear powers accepted commitments to respecting the region’s non-nuclear status and sharing nuclear technologies for peaceful uses, especially those related to development promotion. They also provided negative security assurances, agreeing to never threaten or use nuclear weapons against Tlatelolco’s member states. Thus, Latin America secured nuclear powers’ elusive support for regional nuclear arms control mechanisms. Tlatelolco did a good job balancing contradictory preferences regarding access to nuclear technologies. In the 1960s, nuclear energy supporters promised that this technology could reduce industrialization costs. In the early years of the nuclear age, some proponents argued that certain nuclear undertakings in the grey zone between peaceful and bellicose activities, like nuclear explosions, had promising economic benefits. Some Latin American countries negotiated to guarantee their ability to develop indigenous nuclear enterprises. They were worried about great powers with nuclear capabilities monopolizing technological advancements through nuclear arms controls, denying them access to industrialization tools. The Treaty of Tlatelolco ensures the capacity of Latin American states to build domestic nuclear programs and engage in all peaceful nuclear activities. It reflects these countries’ fear that depending on nuclear powers sharing technology and knowledge would negatively affect their quests to industrialize and promote development. The treaty promotes establishing ties for technological cooperation between nuclear and non-nuclear states. Latin America, especially Brazil and Mexico, referred to Tlatelolco as the example that the NPT should have followed to balance non-proliferation and disarmament. Mexico and Brazil were invited to the Eighteen Nations Committee on Disarmament (ENDC), a group at the United Nations commissioned to draft the NPT. Mexican and Brazilian diplomats came to the ENDC with the lessons they learned during the negotiations of the Treaty of Tlatelolco. The Latin American NWFZ reinforced the US nuclear-weapon monopoly in the hemisphere. However, it limited the threat and use of nuclear force and guaranteed the exchange of nuclear technology from nuclear powers to Latin American countries. For both Mexico and Brazil, Tlatelolco was the ideal response to prevent nuclear proliferation. Both countries tried to extrapolate elements of Tlatelolco to the NPT. Mexicans attempted to become brokers in the NPT negotiations by mobilizing Latin American delegations in the United Nations. As nuclear powers included Tlatelolco elements in the NPT, Mexicans mobilized to gather support for the treaty. Brazilians sought to safeguard the same developmental options in the NPT that they secured in Tlatelolco, especially regarding access to peaceful nuclear technologies. When they faced nuclear powers’ opposition to carrying out certain activities, like peaceful nuclear explosions, Brazilians denounced the NPT as an attempt to limit the industrialization options available for developing countries. We need to focus more on NWFZ NWFZs are a nuclear non-proliferation mechanism that International Relations scholars and policymakers often overlook. Academics and practitioners tend to minimize the role of non-nuclear-weapon states and, thus, of NWFZ in international security. The Treaty of Tlatelolco reminds us that the commitments of non-nuclear-weapon states are fundamental to maintaining the global nuclear order. The Latin American construction of a NWFZ questions the assumption in mainstream scholarly and policy circles that only powerful actors order international politics, especially in the security domain Latin American states actively designed nuclear limits and crafted institutions to enforce them during a moment when they shared a common goal—guaranteeing the security of the region from nuclear arms races and potential nuclear wars. The Latin American participation in crafting the regional NWFZ did not mean harmony of interests. Latin American states and nuclear powers shared common anxieties about the dangers of the nuclear arms race. However, Latin American countries had different opinions about disarmament and access to peaceful nuclear technology, and nuclear powers opposed proposals limiting their security preferences. Thus, Latin America embarked on a laborious process of setting security priorities, crafting compromises, and securing the cooperation of nuclear powers. J. Luis Rodriguez (@luisrodaquino) is a Stanton Nuclear Security Postdoctoral Fellow in the Center for International Security and Cooperation (CISAC) at Stanford University. His research studies how the Global South builds and maintains limits on the use of force in international law and organization. He holds a Ph.D. from the Department of Political Science at Johns Hopkins University.