Political map of South American nations 12 March 1948 (Rio Pact): Following the end of World War II, suspicion and hostility grew between the United States and the Soviet Union. In this so-called Cold War, the US sought to establish anti-Communist alliances around the world to contain the Soviet threat. The first such alliance was the Rio Pact, a treaty signed between the US and the nations of Latin America to safeguard the Western Hemisphere.