Ulysses S. Grant wrote in his memoir that MacKenzie led an army corps at the very end of the battles to capture Lee's army. He wrote, "Griffin, Humphreys, and Mackenzie were good corps commanders, but came into that position so near to the close of the war as not to attract public attention. All three served as such, in the last campaign of the armies of the Potomac and the James, which culminated at Appomattox Court House, on the 9th of April, 1865. The sudden collapse of the rebellion monopolized attention to the exclusion of almost everything else. I regarded Mackenzie as the most promising young officer in the army. Graduating at West Point, as he did, during the second year of the war, he had won his way up to the command of a corps before its close. This he did upon his own merit and without influence." Mackenzie was mustered out of the volunteer service on January 15, 1866. On January 13, 1866, President Andrew Johnson appointed Mackenzie to the brevet grade of major general of volunteers, to rank from March 31, 1865, for services in the Shenandoah Valley campaign and the U.S. Senate confirmed the appointment on March 12, 1866. Mackenzie was known for his harsh discipline and was not well liked by troops serving under him, who called him the "Perpetual Punisher". However, he was respected by his peers and superiors for his skill and abilities, prompting General Ulysses S. Grant to refer to him as the "most promising young officer" in the entire Union army. He had been wounded six times and received seven brevets. Service in the Indian Wars After the Civil War, Mackenzie remained in the regular army and reverted to his permanent rank of captain in the Army Corps of Engineers. Appointed colonel of the 41st U.S. Infantry (later 24th U.S. Infantry, one of the Buffalo Soldier regiments) in 1867, Mackenzie spent the rest of his career on the Frontier. Some officers were reluctant to lead African-American regiments, but Mackenzie did well with the 41st. On February 25, 1871, he assumed command of the 4th U.S. Cavalry at Fort Richardson in Jacksboro, Texas. He led the regiment in the Battle of Blanco Canyon and at the Battle of the North Fork in the Llano Estacado of West Texas. In October 1871, he was wounded a seventh time by an arrow in the