U.S. Involvement in WWII
World War 2 was a 4 year war in Europe. The date where it started is vague, though it is thought it has started when Germany attacks Poland.
In this time, the United State, fearing the mistake of the last World War, chose to stay neutral using a policy that makes it so they will not join the war. Though they are neutral, they help the Allied forces with supplies and men. They officially joined the war during the attack on Pearl Harbor.
They offer lots of technology and strength to the allied forces and they eventually won the war in the last 2 years.