International audienceThis paper argues that the central chapters of Book 4 of Thucydides show the failure of Athens’political initiatives during the summer of 424 BC. In these chapters, Thucydides shows that Athens acceptsinvitations from weak democratic factions in Megara and Boeotia in hopes of imposing new politicalarrangements: the strategy both relies on political affiliations and has political aims. It also has politicaloutcomes, since Athens fails twice in a row, and both attacks result in the consolidation of hostile andoligarchical regimes. The Spartan commander Brasidas was therefore certainly important for Athens’ failures,but not their central cause.Cet article soutient que les chapitres centraux du livre IV de Thucydide montre...