Allan Pinkerton, President Abraham Lincoln, and Major General John A. McClernand; Antietam, Maryland
Photograph from the main eastern theater of the war, Battle of Antietam, September-October 1862.
At Antietam (or Sharpsburg), on Sept. 19, 1862, the casualties numbered 23,000-- nine times greater than those of D-Day in World War II.
The Union victory turned back General Lee's invasion of the North, negated his intent to get Abe Lincoln to sue for peace, and provided a rationale to declare the abolition of slavery.
General McClernand commanded the 1st Division of the 8th Illinois Volunteer Regiment, which fought at Fort Donelson and Shiloh.
In 1861, Allan Pinkerton thwarted a plot to assassinate Presisent Abraham Lincoln, and, at the President's request, started the Secret Service. His Operatives later used a double agent to uncover a Confederate plan to free 8,000 prisoners of war.