How did the civil war affect relations between the sioux and their allies?

Actually, the civil war make their relationship became much worse.

Because of the civil war, the ally has to lose a lot of resources for war supplies and equipment. This led to a situation where the allies no longer able to pay the treaties that they promisd to pay to the Sioux, which eventually ended up in conflict between the two group.

The civil war affected relations between the Sioux Indians and their allies because after the Civil War was over, Native American tribes and Native American nations that had stood with the Confederacy an fought had their government treaties nullified.