The question was prompted by this painting posted over in /r/battlepaintings which shows a person in the bottom left who is dressed in traditional native american garb fighting on the side of the confederacy. It struck me as really odd that a native american would fight for either side in the civil war as they were such a mistreated class by Americans in general. Is it possible they fought for the confederacy in order to stop the US government expansion and hostility towards indians in the west? Did they fight as mercenaries? Was there ever a formal alliance or agreement between belligerents in the civil war and whole indian tribes or was it more individual? What would the indians seek to gain from such an agreement? And finally how were native american soldiers/mercenaries incorporated into the armies, both in how they were treated by soldiers and officers and in what role they served in the fighting? Edit: upon viewing the painting again it seems there a larger number of indian cavalrymen charging in the background as well although it is hard to tell
The civil war was as divisive for some Indian Nations as it was for the United States.
The tribes that were most involved in "national" policies towards the Civil War were the "5 Civilized Tribes" of Indian Territory (Oklahoma). All 5 of these tribes were slave owners, collectively owning about 10,000 slaves.
Source: http://www.freerepublic.com/focus/news/655380/posts
One would think this inclined them to side with the Confederates, but in fact, both the Creeks and the Cherokee were divided and split, with some on each side.
The Union favoring Creeks, under chief Opothleyahola were attacked by Confederates and Cherokee. They retreated towards Kansas in what was called the "Trail of Blood and Ice". They fought three losing battles along the way, before the survivors reached the safety of Union lines.
The Cherokee Nation also had an internal civil war, with Principle Chief John Ross wanting to remain neutral, but Stand Watie wanting to join the Confederates. Eventually, Chief Ross joined the Confederacy, but the Cherokee Mounted Rifles and Ross defected to the Union forces in Kansas soon thereafter.
Watie became a Confederate general and he led two battalions of Cherokee cavalry as well as Creek Osage and Seminole forces in several successful battles. Watie was the last Confederate General to surrender in the Civil War, two months after Robert E. Lee surrendered at Appomattox.
The only other Native American Brigadier General in the Civil War was Union General Ely S. Parker, a member of the Seneca Tribe, who drafted the articles of surrender which Lee signed.
At the surrender ceremony Robert E. Lee said to Parker, "I'm glad to see one real American here." Parker replied, "We are all Americans."
