Harold North Fowler, Commentary on Thucydides Book 5

ἡ ξυμμαχία: to correspond to c. 46. 35 (see on c. 27. 2), for αἱ ξυμμαχίαι of the Mss. ἐγένοντο (not ἐγένετο, as in c. 80. 1 and i. 102. 22, κατέστη) has for its subj. αἱ σπονδαὶ καὶ ἡ ξυμμαχία regarded as a compound subst. of which the pl. αἱ σπονδαί is the most important part; accordingly the following αἱ τῶν Λακεδαιμονίων καὶ Ἀθηναίων refers grammatically only to σπονδαί. Indeed the ξυμμαχία (c. 23) of the Lacedaemonians and Athenians was practically if not formally at an end, since both parties had entered into obligations which conflicted with it.

οὐκ ἀπείρηντο: the treaty was not renounced, i.e. was not regarded as void.

οὐδ᾽ ὑφ̓ ἑτέρων: not by either party. Equiv. to ὑπ᾽ οὐδετέρων. Cf. ii. 67. 34, τοὺς μηδὲ μεθ᾽ ἑτέρων.

Κορίνθιοι δὲ Ἀργείων ὄντες ξύμμαχοι κτἑ.: the conduct of the Corinthians is represented as equivocal from the beginning: “although they were allies of the Argives (see c. 31. 25 ff.), they did not join the alliance with the Athenians.” To this is added the parenthetical sent., ἀλλὰ καὶ . . . οὐ ξυνώμοσαν (see a similar parenthesis in c. 72. 3 f.). This refers, as explanation and confirmation, to the events recorded in c. 29-31: “for that matter, when the Eleans, Mantineans, and Argives had (at their instigation) made an alliance (see c. 29. 1 f. and 31. 24) the year before (πρὸ τούτου), they had not joined it.” (ξυνώμοσαν, aor. in parenthetical clause with the force of plpf.; see on ii. 2. 12. GMT. 19, N. 4; H. 837.) We now learn for the first time that the Eleans and Mantineans had bound themselves to the Argives τοῖς αὐτοῖς πολεμεῖν καὶ εἰρήνην ἄγειν (either when they first became allies of Argos, or by some subsequent agreement of which no mention is made), whereas the Corinthians, who in c. 31. 25 εὐθὺς μετ᾽ ἐκείνους Ἀργείων ξύμμαχοι ἐγένοντο, had confined themselves, in accordance with their invitation to the Argives (c. 27. 13), to an ἐπιμαχία, ἀλλήλοις βοηθεῖν, ξυνεπιστρατεύειν δὲ μηδενί, i.e. to a defensive alliance. Now they declare themselves contented with this treaty (ἀρκεῖν σφίσι τὴν πρώτην γενομένην ἐπιμαχίαν, which is no other than that mentioned in c. 31. 25 f.), and refuse to join in the new alliance with Athens. This Thuc. regards as a departure from their previous connexions (οὕτως ἀπέστησαν τῶν ξυμμάχων) and a return to their old relations with the Lacedaemonians, πάλιν pointing to a renewal of earlier relations (cf. c. 32. 5).

ἀλλὰ καὶ...οὐ ξυνώμοσαν : is properly a parenthesis, for ἀρκεῖν δ᾽ ἔφασαν κτἑ. must explain οὐκ ἐσῆλθον ἐς αὐτάς, and the fact that they had not joined the Eleans, Argives, and Mantineans in their offensive and defensive alliance is merely introduced as an illustration of the half-heartedness of the Corinthians, but is not of sufficient importance to warrant the further explanation ἀρκεῖν δ᾽ ἔφασαν κτἑ. (St. and Schütz think ἀρκεῖν δ᾽ ἔφασαν κτἑ. explains ξυνώμοσαν, and that there is therefore no parenthesis).

πρὸς τούς...γνώμην εἶχον : see on c. 44. 7 and iii. 25. 10.