Answer: President Harry S. Truman
Step-by-step explanation:
The actions given were all undertaken by former President Harry Truman after he took over from President Roosevelt when the latter died in the last year of the second World War.
Truman decided to drop the atomic bombs on Hiroshima and Nagasaki after he realized that a land invasion would cost too many lives. He also supported the development of the Hydrogen bomb which was worse than the atomic bomb and during the Korean War, he refused to drop atomic bombs on China because he saw that it would escalate the conflict.