From This Republic of Suffering: Death and the American Civil War by Drew Gilpin Faust (Knopf, 2008), Kindle Loc. 1679-1700:
Men thrown by the hundreds into burial trenches; soldiers stripped of every identifying object before being abandoned on the field; bloated corpses hurried into hastily dug graves; nameless victims of dysentery or typhoid interred beside military hospitals; men blown to pieces by artillery shells; bodies hidden by woods or ravines, left to the depredations of hogs or wolves or time: the disposition of the Civil War dead made an accurate accounting of the fallen impossible. In the absence of arrangements for interring and recording overwhelming numbers, hundreds of thousands of men—more than 40 percent of deceased Yankees and a far greater proportion of Confederates—perished without names, identified only, as Walt Whitman put it, “by the significant word Unknown.”
To a twenty-first-century American, this seems unimaginable. The United States expends more than $100 million each year in the effort to find and identify the approximately 88,000 individuals still missing from World War II, Korea, and Vietnam. The obligation of the state to account for and return—either dead or alive—every soldier in its service is unquestioned. But these assumptions are of quite recent origin. There have been many revolutions in warfare in the last century and a half. Although perhaps less dramatic than transformations of military technology and organization, changing attitudes toward the dead and missing have profoundly altered the practices and experience of war—for soldiers and civilians alike. Only with the Korean War did the United States establish a policy of identifying and repatriating the remains of every dead soldier. Only with World War I did soldiers begin to wear official badges of identity—what came to be known as dog tags. Only with the Civil War did the United States create its system of national cemeteries and officially involve itself with honoring the military dead. It was the Civil War, as Walt Whitman observed, that made the designation “UNKNOWN” become “significant.”
The dead of the Mexican War received no official attention until 1850, two years after the conflict ended, when the federal government found and reinterred 750 soldiers in an American cemetery in Mexico City. These bodies represented only about 6 percent of the soldiers who had died, and not one body was identified. But with the Civil War, private and public belief and behavior gradually shifted. This was a war of mass citizens’ armies, not of professional, regular forces; it was a war in which the obligation of the citizen to the nation was expressed as a willingness to risk life itself. In its assault upon chattel slavery, the conflict fundamentally redefined the relationship between the individual and the nation. This affirmation of the right to selfhood and identity reflected beliefs about human worth that bore other implications, for the dead as well as the living.
Later in the chapter, Faust notes that military chaplains were frequently counted upon to keep track of the dead, but that neither the Union nor the Confederate military felt any obligation to inform the families of the dead.