Peloponnesian War (431-404 BC)

The Peloponnesian War between Athens and Sparta, brilliantly documented by Thucydides, ended with Athens's complete defeat and the permanent weakening of the Greek city-state system. The exhaustion of the Greek poleis opened the way for Macedonian conquest under Philip II and then his son Alexander the Great — who spread Greek culture across the known world and fundamentally shaped the Hellenistic civilisation that both Rome and early Christianity would inherit.