When apocalyptic war came to Equestria, the Stables were a life raft for the survival of ponykind. And like a life raft, mares and foals were given priority. At least at first. Things balanced out in the Stables once the colts grew up into stallions. Except for Stable 143.

There, fillies grow up into domesticated mares. And the colts? They get to play outside.
The only stallion in the Stable is the Overseer, Craster.
That is how it has always been, and that is how he keeps it.

A crossover with Fallout, with a sprinkling of Game of Thrones. So fair warning to mind the Dark tags before diving in.