E.C. Marchant, Commentary on Thucydides Book 1

11. νεώτερός τις—in ref. to the Aeginetan War. The sing. has attracted the verbs into the sing. in spite of ἐνθυμηθέντες. αὐτά might of course have been omitted, but Thuc. is fond of putting it into the second member of a rel. sentence. (To repeat the rel. is exceptional.)

13. τοῖς ὁμοίοις ἀμύνεσθαι—to requite us with like treatment. ἀμύνομαι in this sense generally implies the paying back of injuries, and here we should expect ἀμείβεσθαι (see crit. note, and cf. L. & S. under ἀμείβομαι). Presently we have an ordinary phrase, τὸ ἴσον ἀνταποδοῦναι: but it may be that, in opposing the Corinthian “δίκαιον” to the Corcyrean “ξυμφέρον,” Thuc. purposely makes the speaker use a word that is properly used of dealings between enemies; the speaker means “They say we are your enemies (see c. 33. 3): you must judge of that by our actions in the past, and pay us for our so-called enmity with the same sort of ‘enmity.’”

15. εἰ πολεμήσει—in the event of war. The Corinthian, like the Corcyrean, insisted on (1) τὸ δίκαιον, (2) τὸ ξυμφέρον, but—as Fr. Muller says—he deals vaguely with the latter topic, since Corinth had clearly less to offer Athens than Corcyra had.

16. ἐν ᾦ—c. 37. 4. ἕπεται=‘is found,’ ‘is there.’ It is a moral sentiment—much like ‘virtue is its own reward’— but not much in point here. Grammatically τις is for τινι, being attracted into the relative clause.