Ohio was the third most populous state when the war started. Much of southern Ohio's economy depended on trade with the South across the Ohio River, which had served for years as passage and a link with the slave states of Virginia and Kentucky. The culture of southern Ohio was closer to those states than it was to northern parts of the state. Throughout the of the war, the Copperhead movement had appeal in Ohio, driven in part by noted states rights advocate, Congressman Clement Vallandigham.
Ohio played a key role in providing troops, military officers, and supplies to the Union army. It raised nearly 320,000 soldiers for the Union army, third behind only New York and Pennsylvania in total manpower contributed to the military. Of these, 5,092 were free blacks. Ohio had the highest percentage of population enlisted in the military of any state. Sixty percent of all the men between the ages of 18 and 45 were in the service. Ohio mustered 230 regiments of infantry and cavalry, as well as 26 light artillery batteries and 5 independent companies of sharpshooters. Total casualties among these units numbered 35,475 men, more than 10% of all the Buckeyes in uniform during the war. There were 6,835 men killed in action, including 402 officers.
