Why Was The Union Capture Of Vicksburg Important?

Vicksburg was of great strategic importance to the Confederates. While
in their hands, it blocked Union navigation down the Mississippi, and
it allowed communication with the states west of the river, upon which
the Confederates depended extensively for agricultural supplies. The
natural defenses of the city were ideal, earning it the nickname "The Gibraltar
of the Confederacy." It was located on a high bluff overlooking a
horseshoe-shaped bend in the river, De Soto Peninsula, making it almost
impossible to approach by ship.