Video: 'Shiloh: Animated Battle Map'

(Monday, April 7, 1862, 5:00 p.m. local time) — The Battle of Shiloh, an early battle in the Western Theater of the American Civil War, fought in southwestern Tennessee, ended in Union victory today when Confederate forces were forced to retreat, ending their hopes of blocking the Union advance into northern Mississippi.

The Union Army of the Tennessee (Major General Ulysses S. Grant) had crossed the Tennessee River and was mostly encamped near Pittsburg. The Confederate Army of Mississippi (General Albert Sidney Johnston, second-in-command P. G. T. Beauregard) made a surprise attack on Grant’s army from its base in Corinth, Mississippi, landing on the west bank of the Tennessee River.

During the battle, Johnston was gravely wounded; Beauregard assumed command of the army and opted not to assault until late in the evening.

Video: 'Ken.Burns.The.Civil.War.2of9.A.Very.Bloody.Affair.' ("Shiloh" at 31:51)

Overnight, Grant was reinforced by one of his divisions stationed farther north and was joined by three divisions from the Army of Ohio (Maj. Gen. Don Carlos Buell).

The Union forces began an unexpected counterattack the next morning which reversed the Confederate gains of the previous day.

The two-day battle, the costliest in American history up to that time, resulted in the defeat of the Confederate army and frustration of Johnston’s plans to prevent the two Union armies in Tennessee from joining together.

Union casualties were 13,047 (1,754 killed, 8,408 wounded, and 2,885 missing); Confederate casualties were 10,699 (1,728 killed, 8,012 wounded, and 959 missing or captured).