Final answer:
The First Battle of Bull Run, also known as First Manassas, was the first major battle of the Civil War, resulting in a Southern victory on July 21, 1861.
Step-by-step explanation:
The first major battle of the Civil War, which ended in a Southern victory, was the First Battle of Bull Run, also known as First Manassas. This battle, which took place on July 21, 1861, near Manassas, Virginia, shattered the North's hopes for a swift and decisive victory over the Confederacy. With both sides anticipating a quick end to the conflict, the reality of the combat served as a harsh awakening to the grim and prolonged nature of the war that lay ahead.