I know that Native Americans were the first slaves used in the New World but were replaced by Africans due to disease and the work conditions that the natives couldn't handle, but I couldn't imagine that Native American slavery would completely die out for a while. Would Native American slaves still be used by anyone as late as the Civil War?
California Natives were enslaved into the 19th century. That can't be said about all tribes but it applies to the many that were affected by the Spanish mission system. It was also legal to sell Natives as slaves when California was established as a state in 1850. I can't say when it ended with any certainty but they (for the most part) didn't get citizenship until early in the 20th century (1924). I'm also not sure about more Eastern tribes but remember most of them would have been forced West by the time of the Civil War so I can't imagine there being a large number of enslaved Natives in that area.