The essay analyzes the evolution of the relationship between the United States and the Soviet Union over a period of about twenty years, from the early 1930s to the mid-1950s. During this period, Washington followed a path that led it to positions diametrically opposed to those initially assumed towards Moscow: from an initial position of benevolent expectation, to economic and military support provided to the Ussr during the Second World War, to a vigilant attention against the former ally born before the defeat of Japan. This soon turned into open distrust that led the US government to prepare for a possible new military confrontation. The essay highlights the various steps that led the White House to develop the doctrines of containment and roll back that characterized the early years of the Cold War.