L'impérialisme athénien, by Jacqueline de Romilly, recently published, is an important contribution to Thucydidean studies; and as foreign books usually not only cost more but take longer to read, it may save time and money to give here a summary of the argument.
The authoress intends her discussion of the main theme to throw light on the vexed question of the genesis of the History; but with this part of the work we are less concerned. It will be enough to say that she believes Thucydides to have been aware of the ἀληθ∊στἁτη πρóφασıς right from the start (roughly, because the events narrated at the beginning of Bk. II, obviously pre-415, exactly correspond to the phraseology of the speeches at the end of Bk. I, which imply that πρóφασıς); that the subsequent insertions are the Pentekontaetia, the second part of the Athenian's speech at Sparta, the Funeral Oration, Pericles' last speech and obituary notice, details of Brasidas (clearly post-Lysander) in Bk. IV, the personality of Alcibiades, and the Melian Dialogue; and that these insertions were made after 404, when the disastrous end of the war unloosed attacks on the Periclean régime.
Her main argument, however, is that Thucydides' real subject was the Athenian Empire; because (i) the ‘real cause’ was Athenian imperialism, which alarmed Sparta; (ii) it is the background to every major event described (e.g. Plataea, Mytilene, Pylos, Sicily); (iii) the speeches fall into two classes: attack on or defence of the Empire; (iv) he ignores home-politics, because in fact party-differences were only one of degree between extreme and moderate imperialists; (v) the work is a homogeneous unit, whereas many never came to regard the war as one (e.g. Andocides, Pax 9; Aeschines, de F.L. 176); and (vi) the two factors which Pericles selected as guaranteeing victory—the fleet and the treasury—are the same as those on which her empire rested.