Which river was valuable to both sides because it cut through the heartland of the South?

The Mississippi River was indeed valuable to both the Union and the Confederacy during the Civil War because it served as a critical transportation route that bisected the South. Control of the river allowed for the movement of troops and supplies, significantly impacting the war's logistics and strategy. The river facilitated trade and the transport of goods, making it vital for economic survival as well.

Additionally, the Mississippi River provided strategic advantages; whoever held control over it could disrupt enemy supply lines while keeping their own secure. The Union's goal of severing the Confederacy’s access to the river was crucial in their broader strategy to isolate and weaken Southern resources and morale, which ultimately played a key role in the war’s outcome. This central position of the Mississippi allowed it to act as both a barrier and a conduit in the conflict, making it invaluable to both sides.