Augustine, Contra Faustum Manichaeum XXII.73-79
"What is the charge brought against war? Is it that some men, who will in any case die sooner or later, are killed so as to establish order for people who will live in peace?... The real evils in war are the love of violence, revengeful cruelty, fierce and implacable enmity, wild resistance, and the lust for power, and such like; and it is generally to punish these things... that in obedience to God or some lawful authority, good men undertake wars... and right conduct requires them to act."