History of the Peloponnesian War

Furthermore, it is hereditary with you when an alien army comes against you to ward it off, alike in your own land and in that of your neighbours; and most of all when the invaders are Athenians and moreover upon your borders.

For in dealing with neighbours, it is always equality of force that guarantees liberty; and when the contest is against men like these, who are trying to enslave not only those near by but those far away, is it not necessary to fight to the very last? We have as a warning example their policy toward the Euboeans across the strait as well as toward the greater part of Hellas, and must realize that, whereas others make war with their neighbours about territorial boundaries, for us, if we are conquered, one boundary beyond dispute will be fixed for our whole land; for they will come and take by force all that we have.

So much more dangerous is the neighbourhood of the Athenians than that of others. Besides, people who in the confidence of strength attack their neighbours, as the Athenians now do, are wont to march more fearlessly against one who keeps quiet and defends himself only in his own land, but are less ready to grapple with him who meets them outside of his own boundaries and, if opportunity offers, makes the first attack.