Cold War - Containment
Many historians say also that the Truman Doctrine marked the American policy of 'containment' - indeed the 1947 speech is sometimes called the 'Truman's containment speech' In this respect, the most famous passage from Turman's speech has become:
"I believe that 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."
In fine line it meant that Communism could keep what it had got, but he would not let it grow any more. This implication is one of America's justifiably resisting - 'containing' - any further Soviet aggression.