Well, the Norse legends say the world will end in a titanic battle between the gods and their enemies, called Ragnarok. I don't see where the book of Revelations has any more credence than any other apocalyptic vision; they're all equally silly.
As for the U.N. what you have is not a united group, but a collective of self-interested nations that use it as a political stage to get what they want out of other nations...it's far from the altruistic ideal it started out as.