Appeasement: At the outbreak of World War II in Europe in 1939, the US government, particularly President Franklin D. Roosevelt, had some domestic support for appeasement policies towards Nazi Germany. Some Americans believed that it would be better to accommodate Hitler's demands in order to avoid a larger conflict.
Unwillingness to confront fascism: Many Americans were unaware of the true extent of Nazi atrocities, and some even held negative views of certain minority groups, leading them to downplay the threat posed by fascism.
Pacifist sentiment: A vocal minority of Americans were committed pacifists, who opposed war on moral and religious grounds. Religious groups such as Quakers, Mennonites, and Jehovah's Witnesses advocated for peace, and some left-leaning intellectuals criticized the militaristic policies of foreign powers.
Distrust of Roosevelt's leadership: Some Americans, especially Republicans and conservatives, distrusted Roosevelt's handling of the economy during the Great Depression, and they suspected that he was trying to lead the country into war.
Sympathy for Germany: There were individuals and organizations in the United States that openly sympathized with Germany, particularly German-American groups and far-right organizations such as the German American Bund.
It's important to note that while there was significant opposition to US participation in World War II, public sentiment shifted throughout the course of events, and many Americans ultimately supported the US joining the war effort after the attack on Pearl Harbor in December 1941.