COLD WAR HISTORY
After World War II, the United States and its allies, and the Soviet Union and its satellite states began a decades-long struggle for supremacy known as the Cold War. Soldiers of the Soviet Union and the United States did not do battle directly during the Cold War. But the two superpowers continually antagonized each other through political maneuvering, military coalitions, espionage, propaganda, arms buildups, economic aid, and proxy wars between other nations.
How It All Began - Addressing a joint session of Congress on March 12, 1947, President Harry S. Truman asked for $400 million in military and economic assistance for Greece & Turkey and established a policy, aptly characterized as the Truman Doctrine. This doctrine & the related "domino theory" would guide U.S. foreign policy around the world for the next 40 years. The "domino theory" was the belief that if one country fell to Communism, in this case the two key states of Greece & Turkey, surrounding countries would fall to Communism, like dominoes. And the number one country pushing Communism was the Soviet Union. President Truman declared, "It must be the policy of the United States to support free peoples who are resisting attempted subjugation by armed minorities or by outside pressures." The sanction of aid to Greece & Turkey by a Republican Congress indicated the beginning of a long and enduring bipartisan Cold War foreign policy. Future presidential administrations would use similar reasoning to justify actions in Korea, Cuba, and Vietnam, among others.
Sources: JFK Library, History.com