Altaterra

Twenty-five thousand people were taken from Earth and never heard from again. What happened to them?
After being delivered to undeveloped world Altaterra three hundred years ago, a new civilization of humans began. Originally high tech, now they live like pioneers.
Kaitja is a peacekeeper living a quiet life in the mountains with his apprentice Xitano. They're chosen to lead an expedition farther over the mountains than people have ever been. What they don't expect to find is an entire society of people previously unknown to them.
Atami is a dutiful, pragmatic member of his tribe until a bloodthirsty chief puts their entire clan in danger. Thrust into a leadership role he never desired, Atami struggles to keep his people alive and earn the respect of both followers and allies.
When these two cultures meet, the entire history of Altaterra is challenged. Those on the ruling council, however, would prefer those secrets remain buried, and will do whatever it takes to keep the discovery silent.