President Harry Truman's address to the United States Congress, and the world, in March 1947 is seen by some historians as marking the start of the Cold War. In it, the President committed the USA to the role of defender of global democracy, and pledged to contain the expansion of the Soviet Union and the spread of communism. The Truman Doctrine, as it became known, led to the establishment of NATO and, later, US involvement in conflicts in Korea and Vietnam. But, as Bridget Kendall discovers, the speech and the policy it set out were by no means inevitable - both were shaped as much by misunderstandings and exaggerated fears as they were conflicting ideologies and the actions of the former World War Two allies. Producer: Simon Tulett Contributors: Melvyn Leffler, Edward Stettinius Professor of History Emeritus at the University of Virginia, USA; Vladislav Zubok, professor of international history at the London School of Economics, UK; Denise Bostdorff, professor of communication studies at The College of Wooster, in Ohio, USA. Credits: Recording of the The RT Hon Winston Churchill extracts from a speech made at Westminster College Fulton Missouri; Truman's address courtesy of the Harry S Truman Library and Columbia Broadcasting System. (Image: Close-up of President Harry Truman as he delivers a speech to Congress. Credit: Bettmann/Getty Images)