Although the Civil War began with the bombardment of Fort Sumter on April 12, 1863, the first major battle took place around a stream called Bull Run near the town of Manassas Junction, Virginia. The Federal army was led by an Ohio native, Irvin McDowell, originally from Columbus. By the end of the day, McDowell's troops were forced to flee back to Washington when Confederate reinforcements arrived in the afternoon. So in the first major battle, Union troops were led by an Ohioan, and lost.
Move ahead to 1865. At Appomattox Courthouse, Virginia, Robert E. Lee surrendered his army to another native Ohioan, Ulysses S. Grant. Grant and other Ohioans played an instrumental role in the Union victories in the Western Theater, and President Lincoln had the wisdom to move Grant to the East and put him in charge of the Union army. While Grant oversaw attacks on Robert E. Lee's forced at places like Cold Harbor and Petersburg, his good friend and Ohioan, William T. Sherman, drove his army all the way to the sea, cutting a swath of destruction along the way.
This section of the Encyclopedia includes entries that cover the places where battles took place and campaigns were waged.