The Other Slavery: The Uncovered Story of Indian Enslavement in America, by Andres Resendez
"In 1839, Captain John Sutter arrived in California and began acquiring Native American slaves from several nations to work the land he purchased. He eventually owned several hundred "Indian slaves," whom he treated notoriously badly even by the standards of fellow slave-owners. The circumstances that let Sutter keep these slaves in an ostensibly free territory are part of the complex political and social forces that Andrés Reséndez sets out to unpack in The Other Slavery. But if the book makes anything clear, it's that the single organizing force was simple: greed, and an absence of empathy that meant a slow genocide for the victims."
Continued here: http://www.npr.org/2016/04/17/471622218/horrors-pile-up-quietly-in-the-other-slavery