For the initial part of World War II in 1939-1941, America remained formally neutral while supporting the Allied forces via the initial implementation of Lead-Lease. The United States has been gradually preparing for the war while maintaining the isolationist policy. The government and ordinary citizens were hesitant about participating in the war due to immense human losses in World War I.
Thus, the nation was divided between isolationists and interventionists who had two opposite perspectives on the role of the United States. Eventually, America entered World War II on December 7, 1941, and several significant factors led to this decision.
First of all, the scale of the war led by Nazi Germany vastly exceeded isolationists’ expectations, as Hitler was continually annexing and conquering territories in Europe. In the span of nine months in 1940, public opinion shifted from 85% support of political neutrality to half of the population recognizing the necessity of US participation in the war.
The fear of German expansion was gradually spreading all over America, and the isolationist movement was losing its followers. As a result, the eventual defeat of France was the major event that revealed the potential danger of Nazi Germany and shifted Americans toward interventionism.
The second factor that helped to propel the United States from isolationism was the Japanese aggression on the Eastern front and in the Pacific. The United States tried to find a diplomatic solution and utilized economic sanctions to stop Japanese operations in Indochina; however, their effectiveness was relatively scarce. Imperial Japan ignored
America’s requests adapted to sanctions and continued pushing the Eastern front, which was the second major event. Lastly, the attack on Pearl Harbor by the Japanese forces was a direct declaration of war that America could no longer ignore. Shortly after the attack, Franklin D. Roosevelt announced that the United States would participate in the war and help the Allied forces.
In the period of 1939-1941, the United States supported the Allied forces with resources; however, the Lend-Lease was officially implemented on March 11, 1941. According to the policy, America assisted Britain, the Soviet Union, and other allies that opposed Nazi Germany. As a result, the United States spent approximately $50 billion to facilitate the campaigns against the Axis powers.
In my opinion, America chose the correct strategy in participating in World War II, focusing its primary forces in Europe but also opposing Imperial Japan in the Pacific. Compared to the Axis armies, the United States had a significant advantage in numbers and technological units. Thus, it was necessary to utilize them and assist the Allied forces in defeating Nazi Germany in Europe.