Mississippi River campaigns
The Mississippi River campaigns, within the Western and Trans-Mississippi Theater of the American Civil War, were a series of military actions by the Union Army during which Union troops, helped by Union Navy gunboats and river ironclads, took control of the Cumberland River, the Tennessee River, and the Mississippi River, a main north–south avenue of transport. The campaign on and along the Mississippi River started in February 1862 with Union forces pushing down from Cairo, Illinois into disputed territory in Missouri and Kentucky and Confederate territory in Tennessee.
Source: Wikipedia — Mississippi River campaigns (CC BY-SA 4.0)