“That war is an evil is a proposition so familiar to every one that it would be tedious to develop it. No one is forced to engage in it by ignorance, or kept out of it by fear, if he fancies there is anything to be gained by it.”
Book IV, 4.59-[2]; "Nobody is driven into war by ignorance, and no one who thinks that he will gain anything from it is deterred by fear." ( trans. http://www.classicpersuasion.org/pw/thucydides/thucydides-passages.php?pleaseget=4.59-64 Benjamin Jowett)
History of the Peloponnesian War, Book IV
Help us to complete the source, original and additional information
Thucydides 76
Greek historian and Athenian generalRelated quotes

“He said that there was one only good, namely, knowledge; and one only evil, namely, ignorance.”
Socrates, 14.
The Lives and Opinions of Eminent Philosophers (c. 200 A.D.), Book 2: Socrates, his predecessors and followers

The Works of Publius Virgilius Maro (2nd ed. 1654), Virgil's Æneis

Books, Islam and the West: A Conversation with Bernard Lewis (2006)

“You can take every one of Spinoza's propositions, and take the contrary propositions, and”
Richard Feynman, in The Pleasure of Finding Things Out (1999), Ch. 9. The Smartest Man in the World
Context: My son is taking a course in philosophy, and last night we were looking at something by Spinoza and there was the most childish reasoning! There were all these attributes, and Substances, and all this meaningless chewing around, and we started to laugh. Now how could we do that? Here's this great Dutch philosopher, and we're laughing at him. It's because there's no excuse for it! In the same period there was Newton, there was Harvey studying the circulation of the blood, there were people with methods of analysis by which progress was being made! You can take every one of Spinoza's propositions, and take the contrary propositions, and look at the world and you can't tell which is right.

“There is only one good, knowledge, and one evil, ignorance.”
Socrates II: xxxi http://www.perseus.tufts.edu/hopper/text?doc=D.+L.+2.5.31&fromdoc=Perseus%3Atext%3A1999.01.0257#note-link14. Original Greek: ἓν μόνον ἀγαθὸν εἶναι, τὴν ἐπιστήμην, καὶ ἓν μόνον κακόν, τὴν ἀμαθίαν
Diogenes Laertius
Variant: The only good is knowledge and the only evil is ignorance.

“Every religion says war is evil, but one way or another they end up playing along.”
Source: The Wine of Violence (1981), Chapter 14 (p. 164)