Why was Petersburg so important to the Confederate capital, Richmond?
Petersburg protected the southern approaches to the Confederate capital of Richmond.
When Petersburg finally fell, Richmond fell. When the union troops broke through the siege lines of the confederate army, General Lee had to retreat. This lead to the immediate fall of the Southern Capital.
The fall of Petersburg by a night attack by 14.000 Union Troops was the last major battle of the American Civil War. General Lee and the army of Northern Virginia would be forced to surrender shortly after the conquest of Petersburg by the northern Union forces.