Without any of the usual bias, describe this man's contribution to the world.
Personally, and don't quote me on this, but I believe Hitler subconsciously showed to the world that a united Europe would never operate without a sole beneficiary. As in, Europe would never be a monolithic force that a lot of idealistic Europeans strived, because the intrinsic differences are so partisan that there will always be a separation of states. This is why the European Union is a mixed bag; with some people wanting Europe to proverbially rise again (not in Hitler's manner, per se); and others who resent it because it's a federation without the practicalities of one. A plural currency still hasn't the set the global precedent. Joint military command is a blanket whitewashed show of power, and nothing more. Europeans countries still act within their own interests.
I think people who value the EU look at it like a quasi-United States. Which Hitler so rightfully showed would never work, and most likely never will. There can only be one.
Without him epic gifs and memes would not exist. Despite how that sounds I'm not joking, b/c what's really more important, millions of people dying or billions of people laughing?