The First Sioux War was a vitally important conflict that helped define Lakota Sioux / white relations; created a closer national unity among the Sioux; and allowed the United States Army to develop new military tactics, which would eventually be used to defeat the Plains Indians. The war influenced future Sioux leaders like Crazy Horse, Spotted Tail, and Sitting Bull. Fought between two expanding peoples, the Sioux and the Americans, the First Sioux War produced two engagements, both worthy of study-the Grattan Fight and Blue Water Creek. The Grattan Fight, a debacle for the army, caused heated debate in Congress, fueled animosity between the army and Indian Bureau, and allowed Secretary of War Jefferson Davis to increase the size of the army. Blue Water Creek, a punitive expedition led by General William S. Harney, completely destroyed two Sioux villages. During the First Sioux War, Harney used new tactics that officers serving on the expedition would later use in the Civil and Indian wars. Stunned by their losses, the Sioux quickly sought peace, but they never forgot the catastrophic lessons learned. For the Sioux, the war helped define a unified response to further white encroachment after the Civil War.