when was this truman doctrine having the most impact?

Answer 1

The Truman Doctrine, which was issued in 1947, essentially set up the guidelines for the Cold War. It established that if the Russians tried to expand their territorial ambitions, the United States would support those who were fighting back.

It was initially applied to Greece and Turkey in 1947, but it's most obvious uses were:
- Berlin Airlift in 1948
http://en.wikipedia.org/wiki/Berlin_airlift

- The Korean War (1950-53)
http://en.wikipedia.org/wiki/Korean_war

- Vietnam War (1957-75)
http://en.wikipedia.org/wiki/Vietnam_war