Forty Thousand in Gehenna is a science fiction novel set in C. J. Cherryh's Union-Alliance universe.
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Forty thousand Union humans and azi (human clones who grow up learning and being psychologically conditioned by "tape", i.e. machine learning) are sent to the newly discovered Gehenna, one of a very few habitable planets. They are unaware that Union intends from the very start to abandon them there; it is inevitable that the planet will fall under the control of the rival Alliance. The throwaway contingent is simply a cheap way to impede the Alliance. The novel tells the stories of a particular azi and his descendants. With the passing generations, distinctions between natural-born humans and the much more numerous second-class azi gradually disappear.
Gehenna turns out to have a sentient species, the lizardlike Caliban. Though the Caliban think in a very different fashion, some of them pair off with humans, forming some sort of mental or emotional link with their partners. (Some humans adapt their thinking to that of the Caliban, living among them as "weirds".) Gradually two very different societies develop: a militaristic, aggressive one and one more peaceful and cooperative.
When Gehenna is discovered by the Alliance, observers and scientists are sent to gather information. During this time, the two competing societies go to war to determine which will be the model for the future relationship between humans and Caliban.
Best part of story, including ending:
C. J. Cherryh is very good at developing truly alien societies. This may be her best yet.
Best scene in story:
The novel is episodic, having to cover much ground (and generations). However, the action really picks up with the war at the end.
Opinion about the main character:
There really isn't a main character. The description I gave was for a scientist whose sympathies lie with the young female leader of the peaceful society who defeats her male counterpart.