I... just... what is WRONG with you hill billies?!

[Weltall]

It's true, some of the native tribes did support the south. The majority in fact, with on a small number of tribes supporting the north. Isn't that bizarre? One would think a little awareness of their own situation might make them opposed to what the south was doing.

As I understand it, the tribes of Oklahoma had sympathies for the South because of lingering (and justified) bitterness over how the United States government treated them.

In the Timeline 191 books, the Five Civilized Tribes were important and respected citizens of the Confederate State of Sequoyah, where some hard fighting took place during the first world war, but the United States eventually conquers and annexes the state (along with Kentucky and parts of Virginia).