What convinced many Americans that the US needed to prepare to enter world War ii?

Many Americans were convinced that the U.S. needed to prepare for World War II due to the escalating aggression of Axis powers, particularly after events like the fall of France in 1940 and the attack on Pearl Harbor in December 1941. Reports of atrocities committed by Nazi Germany and Japan also heightened fears about global security. Additionally, President Franklin D. Roosevelt's push for increased military production and the Lend-Lease Act, which provided aid to allies, reflected a growing recognition of the need for active involvement in the conflict. These factors combined to shift public opinion toward supporting military preparation and eventual entry into the war.