The December 13, 1861, Battle of Allegheny Mountain in Pocahontas County was one of the bloodiest conflicts of the Civil War's first year. More than a month after an October 3 battle at Camp Bartow (known as the Battle of Greenbrier River), the Confederate army stationed at that point withdrew to winter quarters atop the summit of Allegheny Mountain. Possibly believing the Confederates to be demoralized, Union Gen. Robert H. Milroy led a force of about 1,900 troops in an attack on the Confederate brigade which numbered about 1,200 men.

Milroy's advance skirmished with a Confederate scouting party at Camp Bartow on December 12. Early on the following morning, Milroy divided his troops into two columns in an effort to attack both flanks of the Confederate camp simultaneously. The first column marched up the Staunton-Parkersburg Turnpike, arrived near daybreak on the Confederate right, and attacked. The battle raged for several hours before the Federals were forced to withdraw. Shortly after the conclusion of fighting on the right of the camp, the second Union column arrived and attacked the Confederate left. This attack was also unsuccessful. Total Union casualties were 140 killed or wounded and two missing. Confederate casualties were 128 killed or wounded and 34 captured or missing.

Ironically, the Confederate brigade had received orders to withdraw a few days earlier. The failed attack, however, convinced Confederate Gen. W. W. Loring to leave Col. Edward Johnson's force at Camp Allegheny through the winter of 1861—62.