I’m just gonna pull from the Wikipedia summary, which I think speaks for itself:
The group finds that it has not been transported to another world, but instead is in the distant future of their own world. A decadent but technologically advanced black culture keeps either uneducated or castrated white people as slaves. Sexual slavery and cannibalism are widespread and generally accepted. Adolescent girls are sexually exploited as “bedwarmers” by their owners. Other children are bred on ranches for consumption and slaughtered during puberty (when their flesh is considered particularly tasty) or sometimes earlier.
Take the cannibalism out and I would’ve joked “Oh, so they built futuristic Rome”
I legit thought you meant there was a better author called Farnham who wrote a book called ‘freehold’ who got overlooked in his lifetime in favor of Heinlein, lol