It is impossible to understand American politics and diplomacy since Munich without understanding the intellectual world of those Americans who came to maturity in the interwar period. These were the same politicians, policymakers, and diplomats who had experienced the disillusionment of the Versailles system and the folly of isolationism. They had struggled through the Great Depression, which had reduced half of America's population to penury. They witnessed the rise of communism (with its forced collectivization and purges), fascism, and nazism. They recoiled from the West's abandonment of Czechoslovakia to Hitler in 1938 under the aegis of appeasement and were dragged into the second world war of their lifetime, the death toll this time probably reaching 60 million, including 6 million murdered Jews.
They also perceived a shrinking world in which war and peace were judged indivisible—the hard lesson of Munich, learned on both sides of the Iron Curtain. The analogy shaped a generation of diplomacy. Moreover, modern warfare, with its awful weapons of death and destruction and the equally awful contemplation that they could be delivered anywhere with impunity, caused the majority of Americans to rethink past policies and their role in the world. The usually cautious American public placed its faith in the collective security of the fledgling United Nations. The fact that the UN would not or could not play this promised role produced the moment of truth: Would the United States play the keeper of the balance of power? The answer would prove to be yes, launching what W. W. Rostow once described as the "American Diplomatic Revolution."
In 1938 President Franklin D. Roosevelt had been unwilling to involve America in another war, and so had done little to strengthen British and French resolve at the Munich Conference. When Hitler invaded Czechoslovakia in March 1939, the United States reacted with shock and anger. The U.S. ambassador to Italy later recalled how he had expressed America's dissatisfaction with Germany's actions. He told the Italian minister for foreign affairs that "Hitler's performance had greatly shocked American public opinion and that …the brutal methods employed by Hitler in seizing Bohemia and Moravia by armed force had created a profound impression on the United States." Thus, when Hitler finished off Czechoslovakia, the United States lost all hope it had held of appeasement preventing war. The ambassador to France, William C. Bullitt, wrote to the secretary of state describing the feeling there: "The invasion of Czechoslovakia ends definitely all possibility of diplomatic negotiations…. There is only regret that Hitler's action has ended the period when it was still possible to hope that constructive diplomatic action might maintain peace." It became clear that war was imminent and that the policy of appeasement had failed.
By the time war came to America, Roosevelt had fully learned the harsh lesson of appeasement. In his Christmas Eve "fireside chat" of 1943, he assured the public that while the allies stuck together "there will be no possibility of an aggressor nation arising to start another world war…. For too many years we lived on pious hopes that aggressor and warlike nations would learn and understand and carry out the doctrine of purely voluntary peace. The well-intentioned but ill-fated experiments of former years did not work." From this moment on, American presidents would time and again refer to Munich and the appeasement policies of the 1930s as the prime example of what to avoid in the future.
Munich was also an example of what had to be avoided during an election. During the 1944 presidential campaign, American journalists and politicians alike predicted that Roosevelt would lose many votes because of his presumably conciliatory attitude toward the Soviet Union. The Republican Party actually campaigned against the Roosevelt administration's "appeasement" policies, arguing for a tougher stance against the "communist threat." This trend continued throughout the decade, as shown by a March 1946 poll in which 71 percent of the public disapproved of the administration's policy toward Russia, while 60 percent considered their policies toward the Soviets as "too soft."