What was the reason for the 2nd Battle of Bull Run?

The Union Army named their battles after Geographical location nearby. This is why it was named "The Battle of Bull Run."

The Confederate Army named their battles after towns or structures nearby, therefore,

Union-1st Bull Run

Confederate-1st Manassas

Union-2nd Bull Run

Confederate-2nd Manassas

Union-Pittsburg Landing

Confederate-Shiloh

Union-Antietam

Confederate-Sharpsburg

Union- Olustee

Confederate-Ocean Pond