Dark Knight.

Even so, it wasn't until the attack on Pearl Harbor that they were forced to join the war. During their "serious discussions", many people were against joining the World War because it would in the end leave the U.S.A as the most powerful country in the world. With nuclear technology on the way and their rapid advancements in technology, it would have been easy for them to overthrow the Third Reich after the war had ended and liberate many Countries, which would then owe a great loyalty to them and as such, their reach would have extended across Europe as a whole and they would've become extremely powerful. The U.S.A has always been in it for themselves, I doubt they cared much for a country that had, not that long ago, attacked them for not paying ridiculously high taxes.

A lot of people defected from America during that time because they felt that America should be doing something, and if the government as a whole was not up for the idea, they would just go out there and do it themselves. I don't however believe that was any part of the reason for joining the War. The amount of defectees was still minimal compared to the military might and production power they controlled. And it's not as if the largest consumer population in the world would be blockaded for simply not allying others, considering they still were part of the large amount of funding Britain and Canada (Later Russia) were receiving during the war.