Why did Ulysses S. Grant want Vicksburg Mississippi?

After the fall of Memphis and New Orleans in 1862 Vicksburg Mississippi remained a transit point for Confederate supplies across the Mississippi River. The high bluffs which the town sits on are a singular feature of the Mississippi Delta region and made the city a natural fortress for the Confederacy. Control of the town and the bluffs meant control of the Mississippi river and all the commerce and communications that went with it. Therefore the town became the most important strategic objective of the Union Army in the West from December 1862 until the town surrendered on July 4 1863,