The United States was manufacturing a lot of weapons and supplies for other countries in the beginning of the war. Post WW1 they were self isolationist and really the beginning of the 20th century. There was anti WW2 sentiment due to the German-American population. When Pearl Harbor occured the US basically went into total war production. Remember this followed the Great Depression so everyone wanted to work so the mobilization occurred quickly. Group that with the nationalism and the fact that our troops were fresh and we had more resources and people are the reasons the US ended it so quickly. We came in for the last act and dealt the final blows to the Axis. I hope that helped you.
