Эрнст Кассирер (1874-1945) Myth of the State (1946)

Part II The struggle against myth in the history of political theory
VIII The theory of the legal state in medieval philosophy
...Plato had pointed out in his Republic that the rules of conduct which hold for the mutual intercourse between Greek states are not applicable to barbarians. Even in times of war Greeks should always be treated as friends, at least as potential friends, whereas barbarians are natural enemies. "We shall speak of war when Greeks fight with foreigners whom we may call their natural enemies. But Greeks are by nature friends of Greeks, and when they fight, it means that Hellas is afflicted by dissension which ought to be called civil strife.... They should remember that the war will not last for ever; some day they must make friends again."
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