Truman Doctrine has been the source of American hubris for forty years and shows no sign of being retired. To understand the origin and influence of the Truman Doctrine, it is necessary to go back to what the United States was like in world affairs before 1947. Franklin D. Roosevelt found in 1937 as a result of the hostile reaction to his “quarantine speech” against the Japanese aggression in China that the United States was still unwilling to assert itself in international conflicts. In effect, the United States may have been a world power at the outbreak of the Second World War, but it was not equipped like one and it did not act like one. Whatever the bomb or the rhetoric, the United States was effectively forced to share world power with the Soviet Union—and knew it from at least the last quarter of 1945.