The correct answer is D) It made the taking of the Deep South possible.
The other options of the question were A) It cut off supplies coming from England. B) It opened the door for the fall of Richmond. C) A great moral victory was badly needed.
The Union victory at Vicksburg so important for the North in that it made the taking of the Deep South possible.
The episode in the American Civil War is known as the siege of Vicksburg, Mississippi. The Confederate army showed great resistant but General Ulysses S. Grant implemented a good strategy to surround the city with Union troops. The Confederate army had to finally surrender. This was a great victory to the Union because the North could gain control over the Mississippi River, a key river to navigate, transport troops, and send supplies.