"...and we see...the significant word Unknown..."

This excellent PBS "American Experience" documentary, Death and the Civil War, discusses how the war that claimed more American lives than all other wars combined in which Americans fought, demonstrated the national crisis of what to do with all the bodies.

The Civil War was the war that struck the nation's conscience and showed the federal government that it had a duty to identify, bury, re-bury, and send home the remains of American soldiers. That pricking of national conscience was what led to the creation of Arlington National Cemetery and some seventy other national cemeteries.

The war claimed 750,000 lives. Only half of the bodies were identified and given a proper burial.

From the film:
...And everywhere among these countless graves—everywhere in the many soldier Cemeteries of the Nation, (there are now, I believe, over seventy of them)—as at the time in the vast trenches, the depositories of slain, Northern and Southern, after the great battles—not only where the scathing trail passed those years, but radiating since in all the peaceful quarters of the land—we see, and ages yet may see, on monuments and gravestones, singly or in masses, to thousands or tens of thousands, the significant word Unknown. Walt Whitman, 1865.