Much of the difference between the policies of Franklin Roosevelt and Harry Truman stem from the conclusion of World War II and events relating to the Soviet Union's post-war activity.  During World War II, Roosevelt and the other Allies, though skeptical and mistrustful of communism, perceived Soviet Union as the lesser of two evils.  For this reason, when Truman became president on Roosevelt's death within months of the war's close, he was confronted with the territorial aspirations of the Soviet Union, which Americans equated to those of Adolf Hitler.  This distrust and paranoia come out in Truman's policies, the vast majority of which focused on the Soviet Union.  The Truman Doctrine and the Marshall Plan both targeted the slowing and/or halting of Soviet aggression, the former by directly giving aid to ailing European nations and the latter by infusing a great deal of capital into weak European national economies to ultimately allow them stand on their own.  In addition, the Truman administration initiated the Western Military Alliance, culminating in the establishment of NATO.

Roosevelt made far greater strides on the domestic front than his successor managed to do.  With his New Deal, Roosevelt addressed concerns that spanned the social spectrum.  Economically, his policies provided a number of jobs for those out of work, from the Tennessee Valley Authority, to the Civilian Conservation Corps, to the Works Progress Administration.  Socially, he proposed the Social Security Act in 1935, the Wagner Act (National Labor Relations Act)(gave greater bargaining power to labor) in 1935, and the Fair Labor Standards Act (set a minimum wage) in 1938.  In his domestic policy, Truman carried forth those policies begun by Roosevelt, rather than initiate his own.