General Stand Watie was the last CONFEDERATE general to surrender at the end of the American Civil War.
Here is a link: https://en.wikipedia.org/wiki/Stand_Watie
While many Americans have some familiarity with with the enslavement of Black people, likely few have any knowledge of the complexities involving slavery of and by Native Americans. Only recently is research bringing to light this issue.
I have known for a long time of the Black Seminole Scouts, who were Blacks who had lived among and intermarried with the Seminoles in Florida when it was still Spanish, who had then been relocated to “Indian Territory” from which they escaped and went into Mexico. The US Army was fighting the Commanches and Apaches and others along the Mexican border after the Civil War years, so in need of good scouts and trackers, they enticed a number of the Black Seminoles to come ride with the Cavalry, on the promise of land grants etc.
Beyond that I knew that Commanches made slaves of other tribes they captured, and that was not a pleasant thing for the captive, but far better than being a black slave in the South.
Only coming to light recently is the extent of enslavement of Native Americans by white colonist going back to the late 1600’s, and thereafter. Also just how often a tribe might capture other tribe members in war and raids, then sell them to whites.
There is no question slavery went on in some areas of the Americas before whites arrived, but it is also clear that when Whites arrived and began to want more labor for their farms and plantations and households, that they could enslave local tribes and use them OR sell them for African slaves.
The total of Native Americans enslaved over a couple of centuries or longer has been estimated to the in the low millions.
The sorry history of what Europeans and the United States did and continues to do to the First Peoples is at once complex and horrible beyond measure.