Showdown. During the Classical Period (480-323 B.C.E.) the Greeks were at war with each other at least one-third of the time. With this fact in mind it might be tempting to consider the great war between Athens with its allies and Sparta with its allies, which is often called "the Peloponnesian War," as just another among many long struggles. No doubt the brilliance of Thucydides' account of the war has contributed somewhat to heightening its profile for historians. For the Athenians, however, it taught important lessons about the nature of their democracy, its ability to conduct war, and the roles to be played by law and popular sovereignty.

An Unsteady Peace. The peace treaty concluded between Athens and Sparta in 445 interrupted hostilities without resolving the causes of the dispute between the two powers. It gave Athens a...