History of the Peloponnesian War

"To an autocrat or an imperial city nothing is inconsistent which is to its interest, nor is anyone a kinsman who cannot be trusted; in every case one must be enemy or friend according to circumstances. And in Sicily it is to our advantage, not that we should weaken our friends, but that our enemies should be powerless because of the strength of our friends. And you must not mistrust us;

for we lead our allies in Hellas as they are each useful to us: the Chians and Methymnaeans as independent, on the condition of furnishing ships; the majority on more compulsory terms, with payment of tribute in money; others, though islanders and easy to be reduced, on terms of absolute freedom as our allies, because they occupy strategic positions along the coast of the Peloponnese.

So that it is natural that matters here also should be ordered with an eye to our advantage, and, as we say, with reference to our fear of the Syracusans. For they aim at dominion over you, and wish, after uniting you with themselves on the ground of your suspicion of us, then by force, or because of your isolation when we shall have gone away unsuccessful, themselves to rule Sicily. And that is sure to happen if you unite with them; for neither will so great a force, if once combined, be any longer easy for us to handle, nor would the Syracusans lack strength to deal with you if we should not be present.