The Battle of Shiloh (also known as the Battle of Pittsburg Landing) is a battle in the Western Theater of the American Civil War, fought April 6–7, 1862, in southwestern Tennessee.

A Union force known as the Army of the Tennessee (Major General Ulysses S. Grant) has moved via the Tennessee River deep into Tennessee and is encamped principally at Pittsburg Landing on the west bank of the Tennessee River, where the Confederate Army of Mississippi (General Albert Sidney Johnston, P. G. T. Beauregard second-in-command) launches a surprise attack on Grant's army from its base in Corinth, Mississippi.

Johnston is mortally wounded during the fighting; Beauregard takes command of the army and decides against pressing the attack late in the evening.

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

The Union forces begin an unexpected counterattack the next morning, which reverses the Confederate gains of the previous day.

On April 6, the first day of the battle, the Confederates striek with the intention of driving the Union defenders away from the river and into the swamps of Owl Creek to the west

Johnston hopes to defeat Grant's army before the anticipated arrival of Buell and the Army of the Ohio.

The Confederate battle lines become confused during the fighting, and Grant's men instead fall back to the northeast, in the direction of Pittsburg Landing.

A Union position on a slightly sunken road, nicknamed the "Hornet's Nest" and defended by the divisions of Brig. Gens. Benjamin Prentiss and William H. L. Wallace, provides time for the remainder of the Union line to stabilize under the protection of numerous artillery batteries.

Wallace is mortally wounded when the position collapses, while several regiments from the two divisions are eventually surrounded and surrendered.

Johnston is shot in the leg and bleeds to death while leading an attack.

Beauregard acknowledges how tired the army is from the day's exertions and decides against assaulting the final Union position that night.

Tired but unfought and well-organized men from Buell's army and a division of Grant's army arrive in the evening of April 6 and help turn the tide the next morning, when the Union commanders launch a counterattack along the entire line.

Confederate forces are forced to retreat, ending their hopes of blocking the Union advance into northern Mississippi.

The Battle of Shiloh is the battle with the highest number of casualties in American history until the Battle of Stones River, which is surpassed by the Battle of Chancellorsville the next year and soon after, by the three-day Battle of Gettysburg, the highest-casualty battle of the war.