What was the point of the Truman Doctrine?

The Truman Doctrine is the name given to an American foreign policy, and it is very important when talking about the Cold War because it marks the point when the USA chose to directly oppose the USSR and Communism. President Harry Truman issued the doctrine in a speech on 12th March 1947, in hopes that it would stop or slow the spread of Communism throughout Europe. The spread of Communism was seen as a form of expansion of the USSR, which was seen as dangerous by Western leaders. The introduction of Marshall Aid in 1948 added power to the doctrine, because Communist countries would not receive any money or aid from the USA. This pressured some into rejecting Communism, as they would rather have had the aid to rebuild and repair their countries after the war. The power of the USA at the time also intimidated some into rejecting Communism out of fear. In this way the doctrine was as much a piece of propaganda as it was a political policy, and is seen by some as the start of the Cold War.