The Union won anyway and they continued to adapt the blue uniform later on when they were the cavalry subjugating the native Americans.So if the Conferderates had won would they be any less oppressive against the Indians?Considering there was a racist element inside their ranks despite their generals extra- curricular actitivies.It could be they wern't as full of the frontier spirit as their foes up north.However the southern states are much warmer overall.There wasn't any sudden urge to walk into the desert.
Both slavery and states rights played roles. It also was a combination of other factors. If slavery was not in the equation, I would have completely supported the CSA. Secession would have been more justified. Of course, Lee opposed even that. He led the CSA troops out of loyalty to his home state of Virginia. Many other Confederates fought for the same reason. Of course, it's easier to judge individuals in the past when we have the luxury of existing in another place and time. As for Native Americans, some of them indeed fought for the South. Some of them even owned slaves, as did some Black people. Latin Americans and foreign people fought for both sides too. It was quite complicated. There were abolitionists in the South too. One or more areas supported the North. A state (West Virginia), as well as some counties (one in northeastern Tennessee), seceded from the Confederacy. There was virulent racism in the North too, so it's not as simplistic as some history books try to make it out to be.
As for frontier spirit, many people in the southern states descend from people like Daniel Boone and Davy Crockett. The war lasted as long as it did because so many Confederate troops were skilled fighters, riders, shooters, etc.. They were some of the best soldiers in the world. The Union troops contained valiant heroes too.