The Real War

“Future years will never know the seething hell and the black infernal background of countless minor scenes and interiors...the real war will never get in the books....Its interior history will not only never be written—its practicality, minutiae of deeds and passions, will never be even suggested.”

--from The "Real War Will Never Get in the Books"

Whitman is talking about the real war—the real stories from that war, the real people—and acknowledging the fact that none of that will ever make it into history. He says that it is perhaps best that way. It's true that our knowledge of conflicts of the past, including the Civil War, comes in the form of causes and consequences, number of wounded and killed, so-and-so battle took place at so-and-so time and place, etc. However, I don't think Whitman gives himself enough credit as a poet. What he says calls to mind a poem, “The Fallen Majesty,” by W.B. Yeats:

Although crowds gathered once if she but showed her face,
And even old men's eyes grew dim, this hand alone,
Like some last courtier at a gypsy camping-place
Babbling of fallen majesty, records what's gone.

The lineaments, a heart that laughter has made sweet,
These, these remain, but I record what's gone. A crowd
Will gather, and not know it walks the very street
Whereon a thing once walked that seemed a burning cloud. 

In this poem, Yeats elaborates on what the poet does, namely, "record what's gone." I think some of Whitman's poems from the war, "The Wound Dresser," for example, do record the real war, and so it is not lost.