The United States was neutral at the start of World War II. However, we eventually joined the war on the side of the Allies. We were neutral when the war began because we didn’t want to get dragged into the war. Congress had passed very strict neutrality laws that prevented us from selling war materials to countries at war. This was done because there was some thought we entered World War I so that our industries could benefit and make money. The Nye Committee came to this conclusion in the 1930s. People were also concerned that other countries, except Finland, didn’t repay their debts from World War I to us. Thus, there was a strong sentiment to do things and pass laws that would make it harder for us to be involved in world affairs and to enter World War II.
However, things changed dramatically on December 7, 1941. On this day, Japan attacked us at Pearl Harbor. Much of our military in the Pacific was destroyed in this attack. We had no choice but to go to war. A few days later, Germany and Italy declared war on us. Thus, we had to fight them also. Plus, we couldn’t let Britain fight alone in Europe. Based on various events, we went from a policy of neutrality to being an active participant in World War II.
The United States decided to stay away from the onset of World War II due to the prevailing attitudes towards foreign conflict following our involvement and late entry into World War I. Collective wisdom (and political cartoons) argued that involvement did not help our stature in the world, and only led to bankrupt countries unable to pay their war debts. This pragmatic analysis led to a general belief in isolationism, which is a policy of non-intervention in the affairs of foreign countries that advocates self-sufficiency for your own country first and foremost as a way to avoid unnecessary entanglements.