www2.gwu.edu/~nsarchiv/

The National Security Archive is an independent archive with commentary on documents on US foreign policy accessed through the US Freedom of Information Act.

www.mtholyoke.edu/acad/intrel/coldwar.htm

This site provides a comprehensive list of documents relating to the Cold War.

www.mtholyoke.edu/acad/intrel/vietnam.htm

This site provides a comprehensive list of documents relating to the Vietnam War.

https://www.state.gov/misc/112234.htm

This is the official US government archive containing documents on US foreign policy.

http://www.bbc.co.uk/history/worldwars/wwtwo/truman_01.shtml

This is a useful link focusing on the Truman administration and the origins of the Cold War.