Containment, the basic idea surrounding most of the United States’ post-war foreign policies, was proposed by George Kennan in 1947. He had spent time as a US diplomat in the Soviet Union throughout the war, and he believed that if the US took steps to prevent Soviet expansion, the system would eventually break and communism would be crushed. This idea came to be known as Containment.
Containment manifested itself into two forms, one of which was economic. In 1947, Secretary of State George Marshall proposed his Marshall Plan. In this plan, the US would give financial support to all European nations who needed it. This plan was intended to curb the spread of Soviet communism by binding European countries financially to the US.
Containment was also applied politically, as shown in the Truman Doctrine and the formation of NATO. The Truman Doctrine, proposed by President Truman in 1947, promised to aid every country that came under the threat of communism. Truman believed in the Domino Theory; if one nation in a region fell to communism, the others would follow suit. The Truman Doctrine first helped Greece and Turkey escape the Soviet grasp, and again in the Latin American nations of Guatemala and Nicaragua, as well as in Korea and Vietnam. NATO, the North Atlantic Treaty Organization, was an established pact between most non-communist European nations and the US and Canada that provided mutual agreements for protection should one member be attacked.
The Marshall Plan, the Truman Doctrine, and NATO were to be at the center of American foreign policy for the next 40 years during the heat of the cold war. They all revolved around the central idea of containment.