The Athenian general and historian whose account of the Peloponnesian War invented the discipline of history as rigorous political and military analysis — insisting on accurate evidence, rejecting mythological causation, and identifying the deep structural forces that drive states to war in ways that political scientists and strategists still use today.
Thucydides wrote the first work of modern history — meaning the first account of human events that tried to establish what actually happened and why, without appealing to gods or fate. His analysis of why Athens and Sparta went to war ('the growth of Athenian power and the fear this inspired in Sparta') became the template for realist international relations theory. Statesmen have read him for 2,500 years. The 'Thucydides trap' — the tendency of rising powers and declining ones to go to war — is named after him and applied to China and the United States today.