What define the Western Theater are series of campaigning and the outline of land in the United States. The Appalachian Mountains and the famous Mississippi River partially stood for the geography that defines Western Theater. Activities against the Eastern Seaboard and the Gulf Coast were not included. In 1864 and 1865, however, as time passed by, the armies of William Tecumseh Sherman moved to Tennessee. This brought about the expansion of how Western Theater was defined, finally including the Carolinas and Georgia .
The fall of New Orleans happened since the US Navy intervened with the operations. Union forces made the fall even more possible, having the Mississippi River even manipulated almost totally. Second was the Battle of Stones River. In Nashville, there came the need for organizing and supplying all over again. Rosecrans hurried everything up and made everything work faster after taking over Bragg. Behind his exemplary leadership, there came a regrouping in the troops focused on the Nashville Turnpike and was indeed an undeniable defensive perimeter.
Lastly, there were batters in Tennessee and Kentucky which drove Grant to act against Vicksburg, MS. Vicksburg was soon placed on bluff at a crisp and sharp turn in the waters. Halleck gave free control to Grant, paving way for the two-prong attack which included 32,000 men advancing down the Mississippi River. There were another 40,000 people who advanced using the railroad in Mississippi Central. The people in Vicksburg experienced starvation and bombardment from the Union, causing great suffering to civilians and soldiers.
They all wished that General Johnston would extend help being bringing with him reinforcements, but he became too cautious. The attempts on Vicksburg were collectively a turning point of the Civil War in the US.
Ambrose, Stephen. Struggle for Vicksburg: The Battles and Siege That Decided the Civil War. Mississippi: Stackpole Books, 1967. Johnson, Douglas Wilson. The Western Theater of War. H. Holt and Company, 1917.