ὅτι πόλεμός ἐστι ταῖς τ' Ἀθήναις καὶ τῶν πολεμίων ἔστιν οἷς ·

This is another sentence from Rouse’s Greek Boy. I don’t understand the οἷς. Is it a relative pronoun or a demonstrative? I just can’t make out the sense. “Because there is a war against Athens and they have some enemies.” Could I take τῶν πολεμίων as a partitive genitive and translate “some enemies”? Is οἷς a kind of dative of possession. Here is the context:

πολλάκις ἀγγέλλει ἡμῖν ἄγγελος , ὅτι πόλεμός ἐστι ταῖς τ’ Ἀθήναις καὶ τῶν πολεμίων ἔστιν οἷς · ἔχομεν γὰρ πολλοὺς πανταχοῦ πολεμίους , τούς τ’ ἐν τοῖς Μεγάροις καὶ τοὺς ἐν τῇ Αἰγίνῃ καὶ τοὺς ἐν τῇ Βοιωτίᾳ πλὴν τῶν ἐν ταῖς Πλαταίαις · οἱ γὰρ τῶν Πλαταιῶν πολῖται φίλοι εἰσὶ καὶ σύμμαχοι πάλαι τοῖς Ἀθηναίοις .

I think basically you have this right. Here again, ἔστιν οἷς is a unit equivalent to τισίν or ἐνίοις, and ἔστιν doesn’t function syntactically as a verb. I guess you could classify the datives ταῖς τ’Ἀθήναις and ἔστιν οἷς as datives of reference or possession, or something like that. “Athens and some of her enemies are having a war.”

But I think a Greek would write τοῖς τ’Ἀθηναίοις, rather than the name of the city. I think the Greeks would think of the human inhabitants as engaging in warfare, and might even find this Anglicism somewhat ludicrous, as if the buildings marched out onto the battlefield.

Thank you Hylander.