Instead of banishing Nightmare Moon, Celestia successfully separates Luna and the nightmare, and both then seal it in the moon, but the stain of both acts are too much for the Princesses and both perish, but not before giving the prophecy of their return.  1000 years later is a changed Equestria, a splintered government, no advanced school of magic, difficult weather patterns, and a looming threat from the Moon.  Can the reborn Princesses be found in time?  Is friendship still the best hope for a happy tomorrow?  The more things change...