My students learn from Thucydides that Athens was most moderate when under the guiding hand of Pericles. He restrained their pleonexia while lifting them up when things went badly. But the strong leader died and failed to prepare Athens for his successor. Athens became less moderate as time goes on, and they saw their empire threatened even more. The Sicilian expedition ended in disaster, and the perennial anxieties of the Athenians that a single loss would knock out the supports of the Athenian empire came to fruition.