During World War 1 he was in the National Guard as a captain and served in France in command of Battery D of the 129th Field Artillery, 35th Division, American Expeditionary Force, to which he saw numerous action. In his role as a senator, he was in favor of the New Deal was an active member of the Interstate Commerce Committee. Truman was instrumental in passing the Civil Aeronautics Act of 1938 and the Transportation Act of 1940. Truman was head of the Special Committee to Investigate the National Defense Program which gained him favor among the voters. He called for the unconditional surrender of Germany, which came on May 8, and the establishment of the United Nations. During World War II he headed the Senate war investigating committee, which investigated corruption and saved as much as 15 billion dollars.

As president he urged Japan to surrender but his offer was rejected. so after much deliberation ordered atomic bombs dropped on cities that produced weapons of war. They were Hiroshima and Nagasaki and soon after Japan surrendered. Truman favored a United Nations Security Council bill recommending that member states furnish aid to South Korea and later authorized U.S. military intervention. The forces followed the enemy into North Korea into their own territory. Some of his programs included a Social Security, a full-employment program, and better public housing and the removal of slums. Truman called for a military alliance to protect Western nations, the North Atlantic Treaty Organization and was established in 1949. After he retired from office Truman traveled widely and spoke to groups of young people about their civic responsibilities.