“The peace of empires issued from war rests on war. It does not restore to the alienated beings their lost identity.”

Source: 2010s, Gettysburg: The Last Invasion (2013), p. 9

The Second Coming (1980)

Source: Deathworld (1960), p. 112
Context: The compartment was getting crowded as other Pyrrans pushed in. Kerk, almost to the door, turned back to face Jason.
"I'll tell you what's wrong with armistice," he said. "It's a coward's way out, that's what it is. It's all right for you to suggest it, you're from off-world and don't know any better. But do you honestly think I could entertain such a defeatist notion for one instant? When I speak, I speak not only for myself, but for all of us here. We don't mind fighting, and we know how to do it. We know that if this war was over we could build a better world here. At the same time, if we have the choice of continued war or a cowardly peace — we vote for war. This war will only be over when the enemy is utterly destroyed!"
The listening Pyrrans murmured in agreement, and Jason had to shout to be heard above them. "That's really wonderful. I bet you even think it's original. But don't you hear all that cheering offstage? Those are the spirits of every saber-rattling sonofabitch that ever plugged for noble war. They even recognize the old slogan. We're on the side of light, and the enemy is a creature of darkness. And it doesn't matter a damn if the other side is saying the same thing. You've still got the same old words that have been killing people since the birth of the human race. A 'cowardly peace,' that's a good one. Peace means not being at war, not fighting. How can you have a cowardly not-fighting. What are you trying to hide with this semantic confusion? Your real reasons? I can't blame you for being ashamed of them — I would be. Why don't you just come out and say you are keeping the war going because you enjoy killing? Seeing things die makes you and your murderers happy, and you want to make them happier still!"

Songs of the Soul (1971)

[ Link to tweet https://twitter.com/dril/status/361282749086175234]
Tweets by year, 2013

A paraphrased variant of this seems to have arisen on the internet around 2007: It is ... a settled policy of America, that as peace is better than war, war is better than tribute. The United States, while they wish for war with no nation, will buy peace with none.
1810s
Source: Message delivered to Dey Omar Agha, by Isaac Chauncey and William Shaler , summarizing the Treaty with Algiers (1815) http://avalon.law.yale.edu/19th_century/bar1815t.asp, and U.S attitudes and actions in the Barbary Wars, in refusing to pay ransom or tribute to pirates of the Barbary States, as quoted in History and Present Condition of Tripoli: With Some Accounts of the Other Barbary States http://books.google.com/books?id=YMwRAAAAYAAJ&pg=PA46 (1835) by Robert Greenhow, p. 46

The Human Comedy (1943)
Context: Everything is changed — for you. But it is still the same, too. The loneliness you feel has come to you because you are no longer a child. But the whole world has always been full of that loneliness. The loneliness does not come from the War. The War did not make it. It was the loneliness that made the War.

"Those at the top say: peace and war" [Die Oberen sagen: Friede und Krieg] from "A German War Primer" [Deutsche Kriegsfibel] (1937), trans. Lee Baxendall in Poems, 1913-1956, p. 288
Poems, 1913-1956 (1976)

Sometimes erroneously prepended to the opening line "The art of war is of vital importance to the State", but appears to be a variation of the Roman motto "Si vis pacem, para bellum". It's not clear who first misattributed this phrase to Sun Tzu. The earliest appearance of the phrase in Google Books is 1920, when it appeared in a pharmaceutical journal, but no attribution was given then.
Misattributed