Organization of American States - OAS
The Organization of American States is the world’s oldest regional organization, dating back to the First International Conference of American States, held in Washington, D.C., from October 1889 to April 1890. That meeting approved the establishment of the International Union of American Republics, and the stage was set for the weaving of a web of provisions and institutions that came to be known as the inter-American system, the oldest international institutional system.