Dean Gooderham Acheson was an American statesman and lawyer. As the 51st U.S. Secretary of State, he set the foreign policy of the Harry S. Truman administration from 1949 to 1953. He was also Truman's main foreign policy advisor from 1945 to 1947, especially regarding the Cold War. Acheson helped design the Truman Doctrine and the Marshall Plan, as well as the North Atlantic Treaty Organization. He was in private law practice from July 1947 to December 1948. After 1949 Acheson came under partisan political attack from Republicans led by Senator Joseph McCarthy over Truman's policy toward the People's Republic of China.

The Truman Doctrine is an American foreign policy that pledges American "support for democracies against authoritarian threats." The doctrine originated with the primary goal of countering the growth of the Soviet bloc during the Cold War. It was announced to Congress by President Harry S. Truman on March 12, 1947, and further developed on July 4, 1948, when he pledged to oppose the communist rebellions in Greece and Soviet demands from Turkey. More generally, the Truman Doctrine implied American support for other nations threatened by Moscow. It led to the formation of NATO in 1949. Historians often use Truman's speech to Congress on March 12, 1947 to date the start of the Cold War.