Thucydides’ History of the Peloponnesian War examines the conflict between Athens, Sparta and their respective allies from its outbreak in 431 BC. The work begins by considering earlier Greek history and the immediate causes of the war before following military campaigns, diplomatic disputes, political decisions and changes within the rival alliances. Thucydides also includes speeches that present arguments attributed to leading figures and opposing sides.

The narrative gives particular attention to the exercise of power, the pressures of war and the behaviour of political communities during crises. Major episodes include the plague at Athens, the Mytilenean debate, the conflict at Melos and the disastrous Athenian expedition to Sicily. Thucydides aimed to investigate events carefully and distinguish immediate disputes from deeper causes. The surviving work is divided into eight books and remains unfinished, ending in 411 BC, several years before the war concluded in 404 BC.