The Battle of Antietam in Maryland was the first battle of the American Civil War to take place on Northern soil and was the single blooodiest battle of the whole Civil War and in American history generally. On 17 September 1862, the Confederate forces under General Robert E Lee attacked the Union forces of General George McClellan, notwithstanding that they were outnumbered. It was Lee's belief that the Confederacy would need to bring the fight to the North and force the Union to defend its own borders and territories. In the battle, the Union lost 13,000 men to the Confederacy's loss of 10,000 men, but the Confederacy lost a much larger percentage of its total force. Lee's capacity to continue waging war was seriously diminished and, although the war would continue for another 2.5 years, many see Antiteam as the beginning of the end for the South.
A few weeks after the battle, Lincoln attended at Antietam to meet with General McClellan and to urge him to use his army in further attacks upon Lee. In the earlier battle, McLellan had kept 25% of his force in reserve by reason of superior numbers; Lee had been forced to commit his whole army.
Pictured above (click on picture to enlarge):
Allan Pinkerton, Lincoln's bodyguard, of the Pinkerton Detective Agency; Lincoln and General John McClernand at Antietam.