[158] Grant, now realizing that the South was determined to fight and that the war would not be won with one battle, would later write, "Then, indeed, I gave up all idea of saving the Union except by complete conquest."[159]
Shiloh was the costliest battle in American history to that point and the staggering 23,746 total casualties stunned the nation.[160] Briefly hailed a hero for routing the Confederates, Grant was soon mired in controversy.[161] The Northern press castigated Grant for shockingly high casualties, and accused him of drunkenness during the battle, contrary to the accounts of officers and others with him at the time.[162][q] Discouraged, Grant considered resigning but Sherman convinced him to stay.[163] Lincoln dismissed Grant's critics, saying "I can't spare this man; he fights."[164] Ultimately, Grant's costly victory at Shiloh ended any chance for the Confederates to prevail in the Mississippi valley or regain its strategic advantage in the West.[165]
Halleck arrived from St. Louis on April 11, took command, and assembled a combined army of about 120,000 men. On April 29, he relieved Grant of field command and replaced him with Major General George Henry Thomas. 