“We remember what modern warfare is, with no glory in it but the heroism of man.”

1900s, The Moral Equivalent of War (1906)
Context: In modern eyes, precious though wars may be they must not be waged solely for the sake of the ideal harvest. Only when forced upon one, is a war now thought permissible.
It was not thus in ancient times. The earlier men were hunting men, and to hunt a neighboring tribe, kill the males, loot the village and possess the females, was the most profitable, as well as the most exciting, way of living. Thus were the more martial tribes selected, and in chiefs and peoples a pure pugnacity and love of glory came to mingle with the more fundamental appetite for plunder.
Modern war is so expensive that we feel trade to be a better avenue to plunder; but modern man inherits all the innate pugnacity and all the love of glory of his ancestors. Showing war's irrationality and horror is of no effect on him. The horrors make the fascination. War is the strong life; it is life in extremis; war taxes are the only ones men never hesitate to pay, as the budgets of all nations show us.

Presidential address to the first Congress of the AFPFL (20 January, 1946)

1950's, On Revolutionary Morality (1958)
Source: David Schoenbrun, As France Goes (page 234), Harper, 1957.

Individualism and Socialism (1933)

"Body Pleasure and the Origins of Violence" (1975)

Source: End Zone (1972), Ch. 19

Vorkosigan Saga, Mirror Dance (1994)

Note appended to his poem The End of War (1933)
Literary Quotes

Si vede per gli esempi di che piene
Sono l'antiche e le moderne istorie,
Che 'l ben va dietro al male, e 'l male al bene,
E fin son l'un de l'altro e biasmi e glorie;
E che fidarsi a l'uom non si conviene
In suo tesor, suo regno e sue vittorie,
Né disperarsi per Fortuna avversa,
Che sempre la sua ruota in giro versa.
Canto XLV, stanza 4 (tr. B. Reynolds)
Orlando Furioso (1532)