Polybius' History book VI contains the most complete text of Hellenistic Greek political theory that has survived from antiquity and the only extended example of applied political theory. Polybius, an Achaean statesman turned historian, developed a political theory not to justify a political position, advocate an ideal constitution, or speculate on the nature of law, justice, political authority, or the relation of man to the state, but for the practical purpose of explaining and predicting historical events.

Polybius explicitly tells us that the sixth book of his History was intended to serve two functions: (1) to explain Rome's rise to power, specifically, ‘how and by what type of constitution nearly the whole of the inhabited world, in less than 53 years, was overpowered and brought under one rule, that of the Romans’ (1.1.5; III.1.4, 2.6; VI.2.2–3; cf. VIII.2.3; XXXIX.8.7); and (2) to enable astute readers to make intelligent, informed political decisions in a world dominated by Rome (VI.2.8–10), and, in the particular case of political leaders, to govern in such a way as to upgrade and perfect the constitutions of their several states (III.118.10–12). Polybius' attention was therefore directed toward the nature, effectiveness, and destiny of the Roman constitution (VI.11–57).