Ever since Adolph Hitler's invasion of Poland, American and European interwar diplomacy has, with good reason, been judged a failure. Analyzing what went wrong, American historians have been quick to note their own nation's withdrawal from European affairs following the Paris Peace Conference in 1919. Consequently, they have focused great attention on the Senate's rejection of United Statesmembership in the League of Nations, an act which has been seen as both cause and effect of the ensuing years of isolation. Indeed, nonmembership in the Geneva-based international organization came to have—for contemporaries and historians alike—deep symbolic and emotional overtones as well as diplomatic significance, appearing as the quintessence of isolationism itself.