Nazi aggression: Throughout the 1930s and early 1940s, the world had witness the rise of Nazi Germany and its aggressive invasions and annexations of Austria, Czechoslovakia, and Poland. Nazi atrocities, including anti-Semitic persecution and the invasion of other European countries, led many Americans to believe that US involvement was necessary to stop the spread of fascism and protect global democracy.
Economic concerns: The Great Depression had left millions of Americans unemployed, and many believed participating in World War II could stimulate economic recovery. The war effort created new jobs and boosted industrial production, ultimately helping the US economy out of the depression.
Isolationist sentiment shift: While the US had initially pursued an isolationist policy, events in Europe and Asia, such as the German invasion of Poland, prompted a shift in public opinion. Many Americans recognized the potential global threat posed by Nazi Germany and imperialist Japan and believed that US intervention was unavoidable.
President Franklin D. Roosevelt's leadership: President Roosevelt played a crucial role in shaping public opinion and preparing the US for war. He gave fireside chats, held press conferences, and used the media to communicate with Americans about the urgency of the situation and the need for preparedness. His charisma, leadership, and communication skills helped unite the country behind his vision for involvement.
Diplomatic failures: Despite attempts at diplomacy and appeasement efforts by European powers, Nazi Germany's continued aggression made peaceful resolutions seem impossible. The fall of France and the failure of the Munich Agreements convinced many Americans that direct US involvement was necessary to prevent further territorial conquests by Germany and its allies.
Growing awareness of atrocities: As news of the Holocaust and other Nazi atrocities became known , American felt moral obligations to join the fight against barbarism. Public outrage over the inhumane treatment of civilians strengthened the commitment to enter the war on humanitarian grounds.
The combination of these factors compelled a majority of Americans to accept that direct involvement in World War II was necessary to protect the US and its values, safeguard democracy, and prevent the continued spread of totalitarian regimes.