The first book of the History, after a brief review of early Greek history and some programmatic historiographical commentary, seeks to explain why the Peloponnesian War broke out when it did and what its causes were. Except for a few short excursuses (notably 6.54-58 on the Tyrant Slayers), the remainder of the History (books 2 through 8) rigidly maintains its focus on the Peloponnesian War to the exclusion of other topics.