The Civil War, of course, took up a lot of government resources. Because of this, Native Americans in the Midwest weren't paid the way the treaties said they had to be. This led to conflicts between the US and the Indians, including a famous incident in Minnesota that ended with about 40 Sioux being hanged. It was also during the Civil War that the infamous Sand Creek Massacre happened. There were also Indians who fought in the Civil War, mainly on the side of the South. But this had little effect other than on the individuals who fought. Mainly, then, the Civil War helped cause conflicts to erupt because the US Government didn't have the resources to either keep the Indians happy or keep them suppressed.