More clearly than any earlier act, the Truman Doctrine proclaimed that the United States had embarked on a new foreign policy. This new policy of containment would have profound effects on American society and culture. Its immediate aim was to prevent the Soviet Union from moving beyond the line it had reached in Eastern and Central Europe. By 1947 the Truman administration viewed the Soviet Union as powerful, totalitarian, and aggressive, much like Germany and Japan in the 1930s, and believed it must be contained by a policy of firmness and strength.

Two developments appeared to stand in the way. First, the nation had reduced its military force to well below two million people, less than a sixth of those in uniform in 1945. Second, the nation seemed to be slipping back into isolationist attitudes that had prevailed in the 1930s, including hostility toward spending money on foreign...