Origins of the Cold War March 12, 1947 - The "Truman Doctrine" make it United States policy to protect nations threatened by communism June 5, 1947 Secretary of State George C. Marshall calls for a United States plan to help Europe recover from World War 11 June 24, 1948 "The Berlin Airlift" begins as the United States Air Force flies supplies to West Berlin following a Soviet Blockade April 4, 1949 ? 21. Which event completes this timeline? A. The United States offers military aid to South Vietnam under the Domino Theory B. The United States stops the Soviet Union's effort to build a missile base in Cuba C. The United States forms a military alliance with the countries of Western Europe D. The United States establishes a space agency to compete with the Soviet launch of satellites