The Truman Doctrine (1947) marked the beginning of the Cold War. Before Truman gave his famous speech, there was at least a frail hope that conflict with the Soviet Union could be avoided. The resultant conflict, known as the Cold War, was primarily an ideological one, but it also included economic, political, cultural, and military dimensions.
After Germany surrendered in 1945, the Western powers and the Soviet Union tried to work together in Germany and throughout Europe. But they could not agree on arrangements for Germany and Austria. Specifically, the Soviets wanted to spread communism, and the West wanted nations to embrace capitalism and democracy. Communism appealed to many, even in Western Europe. By 1946, the division of Europe into competing ideological blocs became apparent to Winston Churchill. In his "iron curtain" speech, Churchill decried the split in Europe.
By 1947, both Greece and Turkey were in danger from communist aggression. Greece was in the midst of a civil war between pro-West and pro-Soviet groups. Turkey was being pressured by Moscow to grant it rights to the Dardanelles. President Harry Truman gave a speech in which he pledged to help Greece and Turkey avoid communist domination. Washington then spent $400,000,000 to aid those two countries.
The Truman Doctrine was the implementation of America's strategy for the Cold War: containment. During the subsequent years and decades on the Cold War, America fought to "contain" communism throughout the world. Billions were spent on the Marshall Plan. America fought large wars in Korea and Vietnam. Cuba became a Cold War enemy of the United States. Washington supported unsavory regimes during the Cold War and even overthrew governments it opposed—such as that in Iran.