During the American Civil War, the State of Ohio played a key role in providing troops, military officers, and supplies to the Union army. Due to its central location in the Northern United States and burgeoning population, Ohio was both politically and logistically important to the war effort. Despite the state's boasting a number of very powerful Republican politicians, it was divided politically. Portions of Southern Ohio followed the Peace Democrats and openly opposed President Abraham Lincoln's policies. Ohio played an important part in the Underground Railroad prior to the war, and remained a haven for escaped and runaway slaves during the war years.

Camp Chase was a military staging and training camp established in Columbus, Ohio in May 1861 after the start of the American Civil War. It also included a large Union-operated prison camp for Confederate prisoners during the American Civil War.