In 1862, both Union and Confederate armies faced off in two of the bloodiest battles of the Civil War. On April 6, 1862, General Grant’s Union army was ambushed at their encampment by the Tennessee River, by General Johnston’s Confederates. At first, the rebels successfully pushed back the Union army toward the river. But when Johnston was mortally wounded, the Confederates halted their attack for the night. Overnight, Grant was reinforced by one of his own divisions stationed further north and was joined by three divisions from another Union army under Maj. Gen. Don Carlos Buell. This allowed them to launch an unexpected counterattack the next morning which completely reversed the Confederate gains of the previous day. General Beauregard, now in command after Johnston’s death, was unaware that he was now outnumbered and continued with the attack, but by the end of the day on April 7, after losing over 10,000 men, the Confederate army retreated. The Battle of Shiloh was over. Five months later, the Confederate and Union soldiers met again in Antietam. After pursuing the Confederate General Robert E. Lee into Maryland, Maj. Gen. George B. McClellan of the Union Army launched attacks against Lee's army, in defensive positions behind Antietam Creek. At dawn on September 17, Maj. Gen. Joseph Hooker's corps mounted a powerful assault on Lee's left flank. Attacks and counterattacks swept across Miller's Cornfield, and the fighting swirled around the Dunker Church. Despite having superiority of numbers, McClellan's attacks failed to achieve force concentration, which allowed Lee to counter by shifting forces and moving along interior lines to meet each challenge. Despite ample reserve forces that could have been deployed to exploit localized successes, McClellan failed to destroy Lee's army. McClellan had halted Lee's invasion of Maryland, but Lee was able to withdraw his army back to Virginia without interference from the cautious McClellan. His refusal to pursue Lee's army led to his removal from command by President Lincoln in November. Although the battle was tactically inconclusive, the Confederate troops had withdrawn first from the battlefield, making it a Union strategic victory.