… the first great battle of the American Civil War began on this date in 1862. The Union Army, under Grant, was encamped in a poorly chosen position at Pittsburg Landing, Tennessee,. They were attacked by Confederates under Johnston and Beauregard early Sunday, April 6. By the end of the day, Confederates had catured the key position of Shiloh church and driven Union lines nearly to the Tennessee River. Grant, reinforced by Buell, counter attacked Monday morning, regained the lost ground, and forced the Confederates to retreat to Corinth, Mississippi. It was ostensibly a Union victory, though Grant was faulted for a lack of precaution that led to the first day’s disaster. Under criticism to remove Grant, Lincoln replied, “I can’t spare this man, he fights.”
According to James M. McPherson in Battle Cry of Freedom:
The 20,000 killed and wounded at Shiloh (about equally distributed between the two sides) were nearly double the 12,000 battle casualties at [First] Manassas, Wilson’s Creek, Fort Donelson, and Pea Ridge combined.
Shiloh was the beginning of total war.