[Koopaking]

Yes I think the EU is the closest thing we have come to unifying anyone so far. It really would be a stretch to unify the entire world, but there are a couple ways I can think of how this actually could be accomplished, but they are less desirable than we would want. First one would be if a country just took over the world. Invaded everybody else, and made the entire world their own. Sure, it wouldn't be peaceful, but it would be unified. Another way would be for mass genocide of every single human on the planet, besides those of a specific race, ethnicity, and religion. Then they could enjoy all of the new living space, and they could probably get along for maybe a generation or so, before they started fighting. Or we could start a massive war that leaves the world a desolate, uninhabitable wasteland, and we will all be unified in being dead.