Skip to main content

Rio Treaty (1947)

Rio Treaty (1947)

The Rio Treaty (1947) was an agreement binding the republics of the Western Hemisphere together in a mutual defense system. Also called the Rio Pact or the Inter-American Treaty of Reciprocal Assistance, the treaty became effective on December 3, 1948, when two-thirds of the member states had ratified it.

The treaty provided for mutual assistance if an act of aggression threatened the peace of the Western Hemisphere. An act of aggression against one member state was considered an act against all the signatory states, which were obligated to provide assistance and aid. The state or states directly attacked were authorized to determine emergency measures of self-defense that would be examined by a special meeting of foreign ministers, known as the Organ of Consultation, which would meet and agree on collective action. In addition, the Organ of Consultation was authorized to impose sanctions and the use of military force if approved by two-thirds of the ministers.

The Rio Treaty reiterated the principles of the Act of Chapultepec of 1945, but its inclusion of Argentina, which had been purposely excluded in 1945 because of its support of the Axis powers during World War II, reflected the United States's motivation to restructure the Monroe Doctrine into a multilateral defense organization. The principles of the Rio Treaty became the basis of the Pact of Bogotá (1948), which established the Organization of American States (OAS). The Rio Treaty also became a prototype for the formation of the North Atlantic Alliance of 1949. The treaty was used many times during the cold war, notably during the Cuban Missile Crisis.

The treaty lost its influence in 1982 when the United States supported the United Kingdom in its war with Argentina over the Falkland Islands. Yet, the United States invoked the treaty in the aftermath of the September 11, 2001, terrorist attacks on New York City and Washington, D.C., and tried to enlist Latin American countries in its War on Terror. Latin American nations voiced their support for the United States and the Rio Treaty at an OAS meeting after the attacks, but many countries did not join the United States's subsequent wars in Afghanistan and Iraq. In 2002 Mexico left the treaty, arguing that a new agreement needed to be produced.

See alsoOrganization of American States (OAS) .


Cargnelutti, Hugo Luis. Seguridad interamericana un subsistema del sistema interamericano? Buenos Aires: Editorial Centro de Estudios Unión para la Nueva Mayoría, 1992.

Smith, Peter H. Talons of the Eagle Dynamics of U.S.—Latin American Relations. New York: Oxford University Press, 1996.

                                         Lesley R. Luster

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"Rio Treaty (1947)." Encyclopedia of Latin American History and Culture. . 8 Apr. 2019 <>.

"Rio Treaty (1947)." Encyclopedia of Latin American History and Culture. . (April 8, 2019).

"Rio Treaty (1947)." Encyclopedia of Latin American History and Culture. . Retrieved April 08, 2019 from

Learn more about citation styles

Citation styles gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, cannot guarantee each citation it generates. Therefore, it’s best to use citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

The Chicago Manual of Style

American Psychological Association

  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.