Combine facts and answer this: The Battle of Blanco Canyon was the decisive battle of Col. Ranald S. Mackenzie's initial campaign against the Comanche in West Texas, and marked the first time the Comanches had been attacked in the heart of their homeland, Mackenzie, also called Bad Hand, was a career United States Army officer and general in the Union Army during which event?
The answer to this question is:
American Civil War