E.C. Marchant, Commentary on Thucydides Book 1

6. ξυμμάχων τε ἀπόστασις κτλ.—such as revolt of allies, which means in the main withdrawal of the revenues that give them their strength, and erection of a hostile fortress in their country. The first ‘way of war’ was followed by Brasidas in 424 B.C.: the second was not used until 413 B C. (Decelea), but the Athenians had then long feared such an attempt. The context makes it clear that ἀπόστασις implies the bringing about of revolt.

11 ἐπὶ ῥητοῖς—in accordance with fixed conditions; cf. c. 13. 1: the meaning is explained in the following words.

13. ἐν ᾧ κτλ.—and in this case, i e. ‘and this being so, he who enters on war in a calm spirit is safer, whereas he who loses control of himself over it gets more falls.’ The meaning is ‘opportunities arise in war and have to be seized as they arise: it is not well for us to get excited now in thinking out plans of campaign—such cut and dried schemes generally miscariy—but what we must do is to enter on war calmly and take opportunities as they occur.’ ὀργή means excitement, not anger here; cf. 2.11. 7: οὐκ ἐλάσσω euphemism for πλείω, i.e. probably ἢ ὁ εὑοργήτως προσομιλήσας.