The Pan American Union shortly after its construction in 1910
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. (April 2018)
The notion of an international union in the New World was first put forward during the liberation of the Americas by José de San Martín and Simón Bolívar who, at the 1826 Congress of Panama (still being part of Colombia), proposed creating a league of American republics, with a common military, a mutual defense pact, and a supranational parliamentary assembly. This meeting was attended by representatives of Gran Colombia (comprising the modern-day countries of Colombia, Ecuador, Panama and Venezuela), Argentina, Peru, Bolivia, The United Provinces of Central America, and Mexico but the grandly titled "Treaty of Union, League, and Perpetual Confederation" was ultimately ratified only by Gran Colombia. Bolívar's dream soon floundered with civil war in Gran Colombia, the disintegration of Central America, and the emergence of national rather than New World outlooks in the newly independent American republics. Bolívar's dream of American unity was meant to unify Hispanic American nations against external powers.
The pursuit of regional solidarity and cooperation again came to the forefront in 1889–1890, at the First International Conference of American States. Gathered together in Washington, D.C., 18 nations resolved to found the International Union of American Republics, served by a permanent secretariat called the Commercial Bureau of the American Republics (renamed the International Commercial Bureau at the Second International Conference in 1901–1902). These two bodies, in existence as of 14 April 1890, represent the point of inception to which the OAS and its General Secretariat trace their origins.
At the Fourth International Conference of American States (Buenos Aires, 1910), the name of the organization was changed to the Union of American Republics and the Bureau became the Pan American Union. The Pan American Union Building was constructed in 1910, on Constitution Avenue, Northwest, Washington, D.C.
In the mid-1930s, U.S. President Franklin Delano Roosevelt organized an inter-American conference in Buenos Aires. One of the items at the conference was a "League of Nations of the Americas", an idea proposed by Colombia, Guatemala, and the Dominican Republic. At the subsequent Inter-American Conference for the Maintenance of Peace, 21 nations pledged to remain neutral in the event of a conflict between any two members. The experience of World War II convinced hemispheric governments that unilateral action could not ensure the territorial integrity of the American nations in the event of external aggression. To meet the challenges of global conflict in the postwar world and to contain conflicts within the hemisphere, they adopted a system of collective security, the Inter-American Treaty of Reciprocal Assistance (Rio Treaty) signed in 1947 in Rio de Janeiro.
The Ninth International Conference of American States was held in Bogotá between March and May 1948 and led by United States Secretary of State George Marshall, a meeting which led to a pledge by members to fight communism in the western hemisphere. This was the event that saw the birth of the OAS as it stands today, with the signature by 21 American countries of the Charter of the Organization of American States on 30 April 1948 (in effect since December 1951). The meeting also adopted the American Declaration of the Rights and Duties of Man, the world's first general human rights instrument.
The transition from the Pan American Union to OAS would have been smooth if it had not been for the assassination of Colombian leader Jorge Eliécer Gaitán. The Director General of the former, Alberto Lleras Camargo, became the Organization's first Secretary General. The current Secretary General is former Uruguayan minister of foreign affairs Luis Almagro.
Significant milestones in the history of the OAS since the signing of the Charter have included the following: