Only two diagnoses of mental disorder were available to the field surgeon: If a soldier’s behavior was sufficiently bizarre and dramatic, he could simply be classified as one of the 2,603 cases of insanity recorded in the Federal army during the war. But if a soldier was chronically morose, lost his appetite and physical stamina, and was unable to function as well as his comrades, he became a candidate for the more opaque diagnosis of “nostalgia.” Described by surgeons as a particularly debilitating form of homesickness, nostalgia was regarded chiefly as a “camp disease,” marked by lassitude of the spirit, complicated by the boredom of long bivouacs and the rigors of marching. But neither nostalgia nor any other mental ailment was ever attributed to the rigors of combat itself. On the contrary, T. J. Calhoun, an assistant surgeon with the Army of the Potomac, advised his colleagues that if the soldier could not be “laughed out of it by his comrades” or by “appeals to his manhood,” then a good dose of battle was the best “curative.”

At only one Federal hospital could a soldier suffering from what modern clinicians would diagnose as a stress disorder expect any sort of treatment. At Turner’s Lane Hospital in Philadelphia Dr. S. Weir Mitchell investigated neurological traumas that were later recorded in his classic Gunshot Wounds and Other Injuries of Nerves . Several of Mitchell’s case narratives portray wounded soldiers, suffering from a paralysis that Mitchell and his colleagues had difficulty understanding. Although these cases arrived because of their physical wounds—one patient had fallen from a tree, while another had had part of a tree fall on him—their paralysis seems to have had little connection to their wounds. Mitchell would eventually become a novelist as well as a pioneer neurologist; in his very first attempt at fiction, a short story in the Atlantic Monthly based upon his experiences at Turner’s Lane, Mitchell wrote of a soldier, unwounded, who had been made “dumb by explosion.”

Since neither society nor medicine could quite comprehend that the shock of combat caused mental as well as physical damage, soldiers took other measures to alleviate their complaints. An enormous number of them—about two hundred thousand on each side—simply deserted. During combat soldiers could always join the unofficial army of stragglers that attended active campaigning. In battle, units seemed to melt away, only to reconstitute themselves once the fighting had stopped. Hidden away among these numbers were no doubt men who in later wars would have been discovered, diagnosed, and treated for combat stress of one sort or another.

Yet the traditional conceptions of human behavior in combat were nothing if not persistent. Each war seemed to provide proof anew that how men acted in battle depended on heroic virtue. Very much in the manner that a star shines brightest before its extinction, the traditional conception of human conduct in battle took on an intense glow in the years between the Civil War and the First World War. At the very time when foundations were being laid for new psychological understanding of human behavior, there appeared within the world of military thought a set of beliefs that held that no matter what the weaponry, the spirit of the soldier, properly inspired and managed by his courageous officers, would inevitably triumph in battle.

Ironically, this crusade of self-deception was being mounted in those very nations where the greatest advances in psychology were being made. In Paris, where Jean-Martin Charcot’s studies in hysteria at the Salpêtrière attracted the young Sigmund Freud, French military savants would argue before long that élan vital —indomitable will—was the key to victory in battle. While in Germany and Britain theoretical debates over psychology routinely appeared in the medical journals, army officers often spoke of the high casualties that would necessarily be purchased by direct assaults on enemy lines and the corresponding need for men of good breeding and character to lead them.

At the start of World War I, a British journal prophesied few psychological injuries. Instead there was a “mass epidemic of mental disorders” along the fighting lines.

After the Civil War American clinicians found another diagnosis for mental disorders, one that reached a peak of social and medical popularity by the turn of the century. “Neurasthenia”—literally a loss of the finite amount of nervous energy supposed to be inherent in each person—was promoted by Dr. George Beard and found an especially receptive clientele among the upper classes of the industrial Northeast. Neurasthenia was marked by chronic physical weakness, fatigue, stomach disorders, and anxiety. In private practice after the war, Weir Mitchell himself routinely diagnosed neurasthenia in his well-born Philadelphia patients and prescribed a “rest cure” that he had first tried on Civil War soldiers. But the compartmentalization of the medical and military worlds persisted; both Mitchell and Beard had been wartime surgeons, but neither ever seemed to look to combat as a causative factor in his patients’ complaints. Nor, for that matter, did anyone else.