Let's face it: This isn't a show that's bent on portraying historical accuracy. It's all very tongue-in-cheek and it doesn't take itself seriously at all. They're not going to show the real reasons for WWII because this is supposed to be a parody of world relations. It's just not the point. Everyone agrees that WWII sucked no matter who you were, and everyone acted like some manner of douchebag during that period. We all know. Either you're going to love it or hate it. Really no in-between. Personal preference, really.
That being said, I thought it was a pretty good representation of how different countries have acted throughout history. If you can't laugh at yourself and your own country, then super-nationalism wins. I thought the representation of America was spot-on. Also, Russia creeps me out. (In a funny way)