With the surrender of Fort Henry, the Confederates faced some difficult choices. Grant's army now divided Confederate Gen. Albert Sidney Johnston's two main forces: P.G.T. Beauregard at Columbus, Kentucky, with 12,000 men, and William J. Hardee at Bowling Green, Kentucky, with 22,000 men. Fort Donelson had only about 5,000 men. Union forces might attack Columbus; they might attack Fort Donelson and thereby threaten Nashville, Tennessee; or Grant and Maj. Gen. Don Carlos Buell, who was quartered in Louisville with 45,000 men, might attack Johnston head-on, with Grant following behind Buell. Johnston was apprehensive about the ease with which Union gunboats defeated Fort Henry (not comprehending that the rising waters of the Tennessee River played a crucial role by inundating the fort). He was more concerned about the threat from Buell than he was from Grant, and suspected the river operations might simply be a diversion.