After Union Brig. Gen. Ulysses S. Grant captured Fort Henry on the Tennessee River in February 1862, he turned his sights on nearby Fort Donelson on the Cumberland. Western Theater commander Gen. Albert Sidney Johnston sent Buckner to be one of four brigadier generals defending the fort. In overall command was the influential politician and military novice John B. Floyd; Buckner's peers were Gideon J. Pillow and Bushrod Johnson.