Rio Treaty

The Rio Treaty, formally the Inter-American Treaty of Reciprocal Assistance (TIAR, from its Spanish acronym Tratado Interamericano de Asistencia Recíproca), was signed in Rio de Janeiro on 2 September 1947 and entered into force in December 1948. It is the principal collective-security instrument of the inter-American system and predates the North Atlantic Treaty by roughly 18 months, serving as one of its conceptual models.

The core provision is found in Article 3, which states that an armed attack against any American state shall be considered an attack against all, obligating parties to assist in meeting the attack. Article 6 extends the framework to situations short of armed attack—such as aggression that is not an armed attack, extra-continental or intra-continental conflict, or any fact or situation that might endanger the peace of America—allowing the Organ of Consultation (typically the OAS foreign ministers) to agree on collective measures. Article 8 lists possible measures, ranging from recall of diplomats and severance of relations to economic sanctions and use of armed force.

The treaty has been invoked roughly two dozen times, often during Cold War disputes in Latin America and the Caribbean. Notably, the United States invoked it after the 11 September 2001 attacks. Conversely, in the 1982 Falklands/Malvinas War, Washington sided with the United Kingdom rather than Argentina, which many Latin American governments viewed as a betrayal of the treaty's spirit.

Several states have since withdrawn, including Mexico (2002), and the ALBA bloc—Nicaragua, Bolivia, Venezuela, and Ecuador—announced denunciation in 2012, though Venezuela's opposition-led National Assembly moved to rejoin in 2019. The treaty remains legally in force among its remaining parties but is widely seen as a diminished instrument, overshadowed by the broader OAS Charter and ad hoc diplomatic mechanisms.