The Peloponnesian War (431-404 BC) was “a war like no other.” It was a 27 year conflict that brought an end to the fifth century Athenian Golden Age, killed more Greeks in one year than the Persians killed in ten, and, in the end, seemed to solve nothing. The war was of such severity that words lost their meanings. Aggression became courage; prudence became cowardice; moderation became unmanly; understanding was mocked. It was in such an environment shortly after the conclusion of the war that Socrates himself—though he fought bravely during the war—was executed. What caused this war, and why did it escalate to the point where the Greeks became barbarians? The Greeks themselves were unsure. But with so much devastation and pain, not knowing seemed unacceptable. And so it was that Thucydides (c. 460- c. 400 BC), who was himself an Athenian veteran of the war, undertook the first sustained inquiry in history into the origins and course of a single war. Click here for an essay on “Structure and Contingency: The Causes of the Peloponnesian War,” by Jared McKinney, London School of Economics-Peking University.