Thucydides now proceeds to substantiate his statement at 23.5 that he will narrate the causes and disputes leading to the dissolution of the treaty by the Athenians and Peloponnesians (for hitherto only Sparta has decided that the treaty is dissolved, cf. 118.3). In 119-25 the Peloponnesians decide that the treaty is dissolved and that they should go to war); in 126-45 the demands made on Athens and her reply to them during the period of diplomatic exchanges are described. Thucydides then gives his summary in 146, ,which resumes the statement at 23.5.