 He was a close friend of Maj. Gen. Daniel Sickles, commander of the Union III Corps.General de Peyster wrote biographies of III Corps Generals Andrew A. Humphreys and Gershom Mott during the war, and wrote highly of Buford's celebrated usage of light cavalry.After the Civil War, de Peyster was elected as a 3rd Class Companion of the Military Order of the Loyal Legion of the United States in recognition of his efforts to support the Union during the war.