Thucydides

Athenian historian who wrote the History of the Peloponnesian War — the foundational text of political realism in international relations — depicting the conflict between Athens and Sparta as driven by fear, honor, and interest rather than justice or ideology.

Created political realism as an analytical framework — the Melian Dialogue ('the strong do what they can and the weak suffer what they must') and the Sicilian Expedition's analysis of democratic overreach remain the canonical texts for understanding power politics — and Thucydides's method of examining structural causes rather than divine intervention established scientific historiography.