[8] Although his health recovered, family finances declined and McKinley was unable to return to Allegheny. He began working as a postal clerk and later took a job teaching at a school near Poland, Ohio.[9]

Civil War
Western Virginia and Antietam
Rutherford B. Hayes was McKinley's mentor during and after the Civil War.
When the Southern states seceded from the Union and the American Civil War began, thousands of men in Ohio volunteered for service.[10] Among them were McKinley and his cousin William McKinley Osbourne, who enlisted as privates in the newly formed Poland Guards in June 1861.[11] The men left for Columbus where they were consolidated with other small units to form the 23rd Ohio Infantry.[12]
The men were unhappy to learn that, unlike Ohio's earlier volunteer regiments, they would not be permitted to elect their officers; these would be designated by Ohio's governor, William Dennison.[12] Dennison appointed Colonel William Rosecrans as the commander of the regiment, and the men began training on the outskirts of Columbus.[12] McKinley quickly took to the soldier's life: he wrote a series of letters to his hometown newspaper extolling the army and the Union cause.