Final answer:
Leaders in Europe and the United States failed to respond effectively to Nazi Germany's military aggression and persecution of Jews due to factors such as economic hardships, anti-Semitism, isolation, doubt, and appeasement policies.
Step-by-step explanation:
During World War II, leaders in Europe and the United States failed to effectively respond to Nazi Germany's military aggression and persecution of Jews and other groups. In the case of the United States, the government prioritized its own economic hardships caused by the Great Depression, which made it easier to discourage immigration and limit entry visas for refugees. The US government expressed little official concern for Nazi persecutions, and even after President Roosevelt withdrew the U.S. ambassador to Germany after the pogrom against German Jews in 1938, the United States turned away countless Jewish refugees who requested asylum. The 1938 Evian Conference, which aimed to discuss the Jewish refugee problem, was largely unsuccessful. As for European leaders, many were hesitant to confront Hitler due to a combination of doubt, appeasement policies, and hopes of avoiding another war. France and Great Britain, in particular, followed a program of appeasement and underestimated Hitler's desire for conquest.