Final answer:
The U.S. maintained neutrality while supporting the Allies due to historical isolationism, strategic concerns, internal demographics, and economic opportunities. Personal beliefs of presidents Wilson and Roosevelt and a desire to avoid direct conflict also played roles.
Step-by-step explanation:
The United States initially remained neutral in World War I and II due to a combination of historical precedent, strategic concerns, domestic considerations, and a desire to benefit economically from wartime trade without direct military involvement. President Woodrow Wilson wished to keep the US out of World War I to avoid internal division, as many Americans had ties to countries involved in the conflict. During the lead-up to World War II, President Franklin Roosevelt aimed to help the Allies through the "arsenal of democracy" while maintaining neutrality to avoid the domestic turmoil and fulfill the public's desire to stay out of another European war.
Throughout both conflicts, the US sold arms and provided loans mainly to Allied Powers, showcasing a form of support while officially remaining neutral. Such actions were influenced by historical isolationism, the effectiveness of British blockades, and the belief that American economic aid could turn the tide in favor of the Allies without committing troops. This economic engagement eventually evolved from neutrality to a more active stance against the Axis Powers in World War II, especially after the attack on Pearl Harbor.