America's early involvement occurred on September 28, 1940, when Japan, Germany and Italy signed the Tripartite Treaty. This treaty required that any of the three nations had to respond by declaring war should any one of the other three be attacked by any of the Allied nations. This meant that should Japan attack the United States, and the United States responded by declaring war against Japan, it would automatically be at war with the other two nations, Germany and Italy.
Following the Dec 7th attack on Pearl Harbor Roosevelt asked for, and received, a Declaration of War against Japan. Germany followed on December 11th with a Declaration of War against the United States. This action was in accordance with the terms of the Tripartite Treaty signed earlier by Germany, Italy and Japan.
Go back to the facts, the u boats, the German spy networks operating in the US prior to WW2.
We we not friends with the Germans unless you consider the wealthy amoral businessmen like Prescott Bush. The British were our allies. No wonder there is such alarm over American ingnorance.