Life has been harsh since the once-peaceful land of Equestria was invaded by the two-legged monsters who called themselves "humans". These humans have set up systems which has placed Equestria under military rule, Celestia and Luna having been executed in the first few weeks. The remaining populice, the ones who surrendered, now live under the iron boot of humanity, struggling to survive when their new masters suck the lifeblood from the land. Not all humans are bad, is what the older ponies say. The first few humans were kind, helping the ponies, but then the others came, and everything changed.

Note: Yes, I wrote Celestia and Luna as being rather underpowered, but it comes from my argument that they would be hesitant, unless they knew they were being attacked, to even try and defend themselves. Read at your own risk.