A Fearful Slaughter recreates the tense tactical situation of Shiloh—April 6th and 7th, 1862, when a Confederate army under Albert Sidney Johnston launched a dawn surprise attack on the heretofor triumphant Federal Army under Ulysses S. Grant. The result was the first large battle of the war, with over 100,000 men from three armies (Johnston's Army of Mississippi, Grant's Army of the Tennessee, and Federal Reinforcements from Don Carlos Buell's Army of the Ohio) grappling in the woods and swamps of west Tennessee.