E.C. Marchant, Commentary on Thucydides: Book 3

καὶ μήν introduces a new and important point (it never means ‘and yet’).

τοῦ ἑταιρικοῦ—‘the tie of party.’ To this ἑτοιμότερον refers.

ὠφελίᾳ—‘to render help’ cf. the principle συγγνώμη ἀδελφῷ βοηθεῖν. This seems more likely than the usual explanation ‘for the public advantage.’

ξύνοδοι—of political meetings, a word of sinister meaning in the political life of Gk. states, suggesting intrigue and treason. The verb is ἐγένοντο and had Thuc. written ὠφελίας ἕνεκα and πλεονεξίας above, all would have been clear.

ἐς σφᾶς αὐτούς=ἐς ἀλλήλους, a common use.

τῷ θείῳ νόμῳ—i.e. it was not the oaths witnessed by the gods—θεῶν ὅρκοι—that bound them when they exchanged pledges. Cf., for example, Eur. Med. 21 βοᾷ μὲν ὅρκους, ἀνακαλεῖ δὲ δεξιάς, | πίστιν μεγίστην, καὶ θεοὺς μαρτύρεται, and the celebrated passage in the same play, 439 βέβακε δ᾽ ὅρκων χάρις, οὐδ᾽ ἔτ᾽ αἰδὼς Ἑλλάδι τᾷ μεγάλᾳ μένει, with Verrall's notes.