“Older men declare war. But it is youth that must fight and die.”

“Poetry in War and Peace”, p. 129
Kipling, Auden & Co: Essays and Reviews 1935-1964 (1980)

Vol. I; XXV
Lacon (1820)
Variant: Men will wrangle for religion, write for it, fight for it, die for it; anything but live for it.

"Rouge Bouquet" (1918)
Context: In a wood they call the Rouge Bouquet,
There is a new-made grave today,
Built by never a spade nor pick,
Yet covered with earth ten meteres thick.
There lie many fighting men.
Dead in their youthful prime
Never to laugh nor love again
Nor taste the Summertime.

Strange Meeting (1918)
Context: "Strange friend," I said, "Here is no cause to mourn."
"None," said the other, "Save the undone years,
The hopelessness. Whatever hope is yours,
Was my life also; I went hunting wild
After the wildest beauty in the world,
Which lies not calm in eyes, or braided hair,
But mocks the steady running of the hour,
And if it grieves, grieves richlier than here.
For by my glee might many men have laughed,
And of my weeping something has been left,
Which must die now. I mean the truth untold,
The pity of war, the pity war distilled.
Now men will go content with what we spoiled.
Or, discontent, boil bloody, and be spilled.
They will be swift with swiftness of the tigress,
None will break ranks, though nations trek from progress.
Courage was mine, and I had mystery;
Wisdom was mine, and I had mastery;
To miss the march of this retreating world
Into vain citadels that are not walled.

Source: Hainish Cycle, Planet of Exile (1966), Chapter 4 (The Tall Young Men)

All Men are Mortal (1946)