There is a sci-fi book I read in the 90's. It was old back then, so it's possibly been published earlier. It was in English and I suspect the author was either American or British.
From what I can remember of the story, humanity lives in a primitive state on a planet or large spaceship of alien design but they do not know this.
One man is kidnapped or manages to escape and finds out the truth, and then eventually returns back to his people to liberate them.