The Last Castle – Jack Vance (1966)
The effete and decadent humans of the castles on a far-future Earth did not see trouble ahead when they became over-reliant on their alien slaves, the Meks, who did everything for them.
One day the slaves rode up and began to slaughter their masters.
Humans are divided between the elite aristocrats of the castles and those who live outside, considered as barbarians by the decadent castle-dwellers.
One of Vance’s archetypes, the maverick male of the community, sets out to find allies to help him fight the Meks, since the aristos it seems, would rather die than change their ingrained ways and fight to save themselves.
Vance is at his best when writing about the restrictions of entrenched social or religious rules and traditions, and this is a prime example.
It’s a woefully brief novel, but full of Vance’s trademark social detail painted with the flourish of his worldbuilding expertise.