History of the Peloponnesian War

"To an individual, however, who has absolute power, or to a state that holds dominion, nothing is inconsistent that is profitable, nothing reckoned as kindred that does not command confidence; but in every case, as opportunity may serve, you must become either a foe or a friend. And in our case, our advantage here consists in this,—not that we should reduce our friends to weakness, but that, owing to the strength of our friends, our foes should be powerless. Nor ought you to doubt this.

For even in the case of our allies in those parts, as they are severally useful to us, so we govern them; the Chians and Methymnaeans as independent, on condition of their supplying ships; the greater part of them on more stringent terms, subject to contribution of money; but others, although they are islanders and easy to reduce, as allies on terms of entire freedom, because they he in favourable positions around the Peloponnese.

So that here also it is natural that we should regulate them with an eye to our advantage, and, as we say, with reference to our fear of the Syracusans. For they are aiming at dominion over you, and wish, after uniting you on the strength of your suspicions of us, themselves to sway the empire of Sicily, by force, or through your forlorn condition, when we have departed without gaining our object. And it must be so, if you unite with them; for neither will so great a force, when united, be any longer easy for us to manage, nor would these men want strength to deal with you, when we were not here.