Can you guess the war? The battle? The author?
Never mind if you cannot...the sentiments in the letter are timelessly sad and poignant, and could pretty much apply to any conflict since "civilized" societies began fighting.
“It is the night before a battle. The enemy, [city name], and its mighty entrenchments lie before us, the river between—at tomorrow’s dawn our troops will assay to cross, and the guns of the enemy will sweep those frail bridges at every breath….I thought I could almost hear the slow flap of the grim messenger’s wings, as one by one he sought and selected his victims for the morning. Sleep weary one, sleep and rest for tomorrow toil.”
--Clara Barton, 12 Dec 1862, writing to her cousin Vira, the night before the American Civil War battle of Fredericksburg (VA). She pioneered the notion of volunteer medical field work at Civil war battles, the forerunner of today’s Red Cross.