Here are two possibilities for you.

1. We really don't know the full story on them, what we know is just from the people who won the war, when you win you can say whatever you want, we already know how the news will portray someone or some country as some super villain.

2. There are pictures of Adolf Hitler after the war in America, there's a possibility he didn't die and they let him live out his life in America.

Operation Paperclip.

It was a secret operation that allowed Nazi scientists to work for the United States and they will be forgiven for all their crimes.