An eighteen-year-old McKinley volunteered for the Union forces in his native Ohio. He joined the 23rd Ohio Volunteer infantry in June 1861. He served more than four years during his service. He rose from the rank of private to brevet major. He saw action in numerous Civil War battles, including the Battles of Opequon, Cedar Creek, Antietam, Kernstown, Berryville, and Clay’s Mountain. His commander for part of his service was none other than Rutherford B. Hayes—the future nineteenth president of the United States and a fellow Ohioan.