Act of Chapultepec, agreement adopted at Chapultepec Castle, in Mexico City, by the Inter-American Conference on the Problems of War and Peace (also called the Chapultepec Conference), which met from February 21 to March 8, 1945. The conference was attended by all the nations of North and South America except Argentina. The signatories agreed to a mutual defense in World War II against aggression toward any one of them. Declarations of a similar nature directed against aggression by non-American countries had been adopted at various times by the American republics. The novel feature of the Act of Chapultepec was that it was aimed also at aggressive acts on the part of an American state toward other American states. This feature of the agreement was inspired by fear of the militaristic dictatorship in Argentina that had been sympathetic toward the Axis powers during the war. Argentina, however, signed the act a few weeks later and declared war on Germany. The Act of Chapultepec also provided for a treaty to be drafted after the end of World War II continuing into the postwar period the guarantees of the act concerning aggressors. The treaty pledge of the act was fulfilled in 1947 by the Treaty of Rio de Janeiro.