My dad fought the Nazi's they lost. The world knows it. What is the deal with their recent resurgence?

There is no "recent resurgence".

• 1. Nazis never went away. Underground Nazi groups, as well as fully fledged Nazi political parties were common throughout post-WWII Europe.
• 2. The people fighting the Nazis weren't ideologically much better than them. The Americans were still racist as fuck. The British and the French were imperialist world dominators. All of these allies were involved in their own genocides. The Soviets believed in sacrificing huge swaths of their own people to accomplish "great leaps forward".
• 3. Nazism and similiar ideologies are fundamentally based on in-group bias, and that is just something psychological. There will always be people who are more open to others and people who are less open to others.
• 4. If you look at recent wars, you will see that even the non-Nazi, "moderate", "liberal", "centrist" political parties can have blood on their hands and be complicit in atrocities very much reminiscent of the evil the Nazis committed.

I think the bottom line is, you have to unlearn a lot of the just-so narratives that you have been taught about the world.