The reason Black soldiers were called "Buffalo Soldiers" was because their kinky hair reminded Native Americans of the buffalo's curly shoulder fur. 186,000 Black soldiers had fought over the course of the Civil War, and the Army threw those still in service against the Native American uprising in the West. The soldiers were formed into segregated units, the 9th United States Cavalry, the 10th United States Cavalry, and the 24th, 25th, 38th, 39th, 40th and 41st Infantry Regiments

Negro soldiers thankfully didn't participate in the many massacres of Native Americans of the time as the Army didn't trust them to slaughter those the government felt the soldiers could sympathize with.

On a related note, the reason General John J. "Blackjack" Pershing got his nickname was because he commanded negro soldiers during his early days as an officer on the frontier fighting the Sioux and Apache tribes from 1886 to 1898. Black soldiers weren't allowed to become officers.