Fallout: Horse Country

Once upon a time, in the magical land of Equestria...

...There was a time when ponies were friends, but everything changed when the Zebra nation attacked. Everyone got jealous of each other even though they had the same number of things (172), so they started taking stuff (and also losing stuff because, from that point onwards, they all still had 172 things). That lead to a big war where Equestria attacked the zebras. The end of the world was predictable in that ponies and zebras shot lots of bombs at each other, making the world a really bad place. The details are trivial and pointless. The reasons, as always, purely our own. Almost every pony and zebra died because of it. Some idiot mare snapped, causing her to make a big weapon to kill the enemies, but she didn't realise it was more dangerous than she thought, and ended up being the cause of the war. God pissed on the living creatures below his cloudy domain and then set them on fire. They almost all dissolved, turning into a poisonous gas called Helium. Then the sun disappeared.

...But it was not, as some philosophers and priests had claimed, the end of the world. Instead, the apocalypse was only the prologue for another bloody chapter in pony history. Before the end of the war, Scootaloo helped to build a bunch of giant metal houses underground, which prevented a lot of ponies from dying, called Stables. If they tried to get past the black suited FBI personnel and succeeded, however, they would find a hell of a lot of wasted food wrappings everywhere. I mean, they didn't even help the ponies who ate them, because they were all piled up around the exit. But, unfortunately for the residents of Stable 2, when the Overmare closed the giant steel door, she accidentally locked the keys out, so they were pretty much boned.

Fallout: Horse Country