the Confederacy because it signaled the collapse of serious Confederate threats of victory. Lee's army suffered 28,000 casualties (versus Meade's 23,000). Western theater The Western theater refers to military operations between the Appalachian Mountains and the Mississippi River, including the states of Alabama, Georgia, Florida, Mississippi, North Carolina, Kentucky, South Carolina, and Tennessee, as well as parts of Louisiana. Background Army of the Tennessee and Army of the Cumberland The primary Union forces in the Western theater were the Army of the Tennessee and the Army of the Cumberland, named for the two rivers, the Tennessee River and Cumberland River. After Meade's inconclusive fall campaign, Lincoln turned to the Western Theater for new leadership. At the same time, the Confederate stronghold of Vicksburg surrendered, giving the Union control of the Mississippi River, permanently isolating the western Confederacy, and producing the new leader Lincoln needed, Ulysses S. Grant. Army of Tennessee The primary Confederate force in the Western theater was the Army of Tennessee. The army was formed on November 20, 1862, when General Braxton Bragg renamed the former Army of Mississippi. While the Confederate forces had numerous successes in the Eastern Theater, they were defeated many times in the West. Battles The Union's key strategist and tactician in the West was Ulysses S. Grant, who won victories at Forts Henry (February 6, 1862) and Donelson (February 11 to 16, 1862), earning him the nickname of "Unconditional Surrender" Grant, by which the Union seized control of the Tennessee and Cumberland Rivers. Nathan Bedford Forrest rallied nearly 4,000 Confederate troops and led them to escape across the Cumberland. Nashville and central Tennessee thus fell to the Union, leading to attrition of local food supplies and livestock and a breakdown in social organization. Leonidas Polk's invasion of Columbus ended Kentucky's policy of neutrality and turned it against the Confederacy. Grant used river transport and Andrew Foote's gunboats of the Western Flotilla to threaten the Confederacy's "Gibraltar of the West" at Columbus, Kentucky. Although rebuffed at Belmont, Grant cut off Columbus. The Confederates, lacking their gunboats, were forced to retreat and the Union took control of western Kentucky and opened Tennessee in March 1862. At the Battle of Shiloh, in Shiloh, Tennessee in April 1862, the Confederates made a surprise attack that pushed Union forces against the river as night fell. Overnight, the Navy landed additional reinforcements, and Grant counter-attacked. Grant and the Union