The Army of Northern Virginia was the most successful of any Confederate army during the American Civil War. It was the main Confederate fighting force in the Eastern Theater of the American Civil War. The army often fought against the Union Army of the Potomac. The army was led by several generals during its early history, but was best known for its final leader, General Robert E. Lee, who took over in June of 1862. For that reason it was often called "Lee's army".