Foreign Policy from Roosevelt to Truman

You may read about the foreign policy changes enacted in the transition from the Roosevelt administration to the Truman administration here:
https://millercenter.org/president/truman/foreign-affairs

You can also read about Truman’s decision to use the atomic bomb here:
https://www.nps.gov/articles/trumanatomicbomb.htm
or hear about it from Truman himself:

If you’re interested in the big picture of American foreign policy, you may be interested in this CrashCourse video: