Most characterizations of the United States in the interwar period suggest that the country was inactive, isolationist, and unresponsive to potential threats to international security.

I argue that this characterization is so misleading as to be useless: American isolationism is a myth. Very few American politicians could be considered genuine isolationists during this period. The two-thirds rule for treaty ratification in the Senate, which allowed a minority to prevent ratification of the Treaty of Versailles, created the impression of isolationism; the widespread belief prior to the fall of France that Nazi Germany posed no serious military threat made America’s modest preparations rational, not isolationist.