From Ohio History Central
During the American Civil War, the Army of the Potomac was the North's primary army operating in the East. Organized in July 1861, this force confronted the Confederacy's Army of Northern Virginia throughout the conflict.
Despite having superior numbers, the Army of the Potomac suffered numerous defeats during the war's first years. The Battle of First Bull Run in 1861, the Peninsula Campaign and the Battle of Fredericksburg in 1862, and the Battle of Chancellorsville in 1863 were all Northern defeats. The Army of the Potomac did succeed in stopping the Army of Northern Virginia's invasions of the North at the Battle of Antietam in 1862 and the Battle of Gettysburg in 1863, but victories during the conflict's first three years were few for the Army of the Potomac.