I think the context can give help. Having an enemy ready to attack influences the internal life of a city, making it more coherent and ordered. After the battle of Marathon and before the next Persian attack, there was even more friendship in Athens, since Athenians thought that they could rely only on themselves and in Gods. See www.ellopos.net/elpenor/greek-texts/ancient-greece/plato/plato-laws-2.asp?pg=10">Part 2, Page 10. Read also www.ellopos.net/elpenor/greek-texts/ancient-greece/plato/plato-laws-2.asp?pg=15">Part 2, Page 15, where Plato explains why naval power harmed the Athenian life.

In general, pay close attention to the context, several pages around the references to the battles.