"I would not have the anniversaries of our victories celebrated, nor those of our defeats made fast days and spent in humiliation and prayer; but I would like to see truthful history written."--U. S. Grant
On April 6-7, 1862 a battle was fought in Tennessee that prefigured just how bloody and terrible the American Civil War would be, and how, and by whom, it would be won.
The war had been going on for nearly a year, and there had been a number of battles already. However, even the notorious rout at the First Battle of Bull Run had not been as ghastly as Shiloh proved to be. The Union had 28,450 troops at Bull Run, and suffered 2,650 casualties (this includes the total of killed, wounded, captured or missing). The South had 32,230 troops, and 1,981 casualties. Fewer than one in ten of those at Bull Run were casualties, and of those about 850 were killed. Contrast this with Shiloh, where the combined troop numbers were about 110,000, and casualities were just under 24,000, or roughly 1 in 4--and just under three thousand were killed. In one battle. For a bit of perspective the total number of U.S. soldiers killed in Afghanistan is just under two thousand.
Initially the war had seemed to be going the way the South expected, but in January 1862 that started to change. The first major victory for the Union forces came at Mill Springs, Kentucky, where General George H. Thomas defeated Confederate troops under Crittenden and Zollicoffer. Casualties were realtively few, especially by later standards, although among them was Zollicoffer, who was killed, and Crittenden's career (he was accused of being drunk when he had to assume command). The next Southern disasters were in February, when Grant's troops took Fort Henry, and then Fort Donelson. The latter pretty certainly fell quickly due to the incompetent leadership of a pair of "political" generals, who fled to safety leaving the capitulation to a poor regular army general, an old friend of Grant's. All of this meant that the Union had an excellent chance of destroying the hold of the Confederacy on the state of Tennessee and had driven them out of the territory of Kentucky (which had not seceeded, but had been invaded). The Confederate general in charge of the troops in the area, Albert Sidney Johnston, recognized his bad position and had withdrawn from Nashville and had forces concentrated at Corinth, Misssissippi to the South, and Murfreesboro, in eastern Tennessee. Grant intended to go after Johnston's forces in Corinth, and headed down the Tennessee River from Forts Henry and Donelson. They had reached Pittsburg Landing and camped there to await General D. C. Buell's forces before proceeding down to Corinth, about 20 miles away. Grant was so intent on attack that it never crossed his mind the Confederates might come after him instead of the other way 'round. On April 6th Johnston launched his surprise attack, and during the course of a hard fought day the Confederates had a good deal of success, but did not succeed in routing the Union. By the end of the day they had captured the bivouac area, and tents, formerly occupied by Sherman, and had also captured General Prentiss and over 2000 of his men. The fighting stopped at sunset, and the Confederate commanders moved into Sherman's quarters.
There were a mass of disorganized Union "stragglers" milling around at Pittsburg Landing, which looked pretty bad. However, also arriving at the Landing that afternoon and evening were the first of Buell's troops. Furthermore, Lew Wallace's division had gotten lost the preceeding day, but finally showed up, ready to fight after that day's fight was over. So Grant would have fresh troops the following day. He was confident that they would defeat the Confederates. Furthermore, the Confederate commander General Johnston had been killed in mid-afternoon, leaving Beauregard in charge--although Beauregard probably thought he should have been in charge to start with, the death of the commander throws everything off. Also, the Confederate cavalry genius Nathan Bedford Forrest had done a bit of reconnoitering in the evening of the sixth and realized that Buell's men had started arriving, but he was unable to find anyone to report this to.
It turned out that Grant's seemingly irrational confidence was justified: the next day, April 7th, the Union troops did indeed defeat the Confederates. Due to exhaustion they were unable to mount an effective pursuit, but they had won a victory, one that was celebrated in the North, before it began to sink in just how high the cost had been. And the South began to realize that the North would fight, and fight very hard indeed. Their conviction that the Southern fighting man was worth 3 or more of those money-grubbing Yankees had finally met reality, it was a bitter pill to swallow.
Here in 1862 were some fields and a house or two; now there are a national cemetery and other improvements.--Ambrose Bierce, an infantryman at Shiloh