<P> The Peloponnesian War reshaped the ancient Greek world . On the level of international relations, Athens, the strongest city - state in Greece prior to the war's beginning, was reduced to a state of near - complete subjection, while Sparta became established as the leading power of Greece . The economic costs of the war were felt all across Greece; poverty became widespread in the Peloponnese, while Athens found itself completely devastated, and never regained its pre-war prosperity . The war also wrought subtler changes to Greek society; the conflict between democratic Athens and oligarchic Sparta, each of which supported friendly political factions within other states, made civil war a common occurrence in the Greek world . </P> <P> Greek warfare, meanwhile, originally a limited and formalized form of conflict, was transformed into an all - out struggle between city - states, complete with atrocities on a large scale . Shattering religious and cultural taboos, devastating vast swathes of countryside, and destroying whole cities, the Peloponnesian War marked the dramatic end to the fifth century BC and the golden age of Greece . </P> <P> As the preeminent Athenian historian, Thucydides, wrote in his influential History of the Peloponnesian War, "The growth of the power of Athens, and the alarm which this inspired in Lacedaemon, made war inevitable ." Indeed, the nearly fifty years of Greek history that preceded the outbreak of the Peloponnesian War had been marked by the development of Athens as a major power in the Mediterranean world . Its empire began as a small group of city - states, called the Delian League--from the island of Delos, on which they kept their treasury--that came together to ensure that the Greco - Persian Wars were truly over . After defeating the Persian invasion of Greece in the year 480 BC, Athens led the coalition of Greek city - states that continued the Greco - Persian Wars with attacks on Persian territories in the Aegean and Ionia . What then ensued was a period, referred to as the Pentecontaetia (the name given by Thucydides), in which Athens increasingly became in fact an empire, carrying out an aggressive war against Persia and increasingly dominating other city - states . Athens proceeded to bring under its control all of Greece except for Sparta and its allies, ushering in a period which is known to history as the Athenian Empire . By the middle of the century, the Persians had been driven from the Aegean and forced to cede control of a vast range of territories to Athens . At the same time, Athens greatly increased its own power; a number of its formerly independent allies were reduced, over the course of the century, to the status of tribute - paying subject states of the Delian League . This tribute was used to support a powerful fleet and, after the middle of the century, to fund massive public works programs in Athens, causing resentment . </P> <P> Friction between Athens and the Peloponnesian states, including Sparta, began early in the Pentecontaetia; in the wake of the departure of the Persians from Greece, Sparta attempted to prevent the reconstruction of the walls of Athens (without the walls, Athens would have been defenseless against a land attack and subject to Spartan control), but was rebuffed . According to Thucydides, although the Spartans took no action at this time, they "secretly felt aggrieved". Conflict between the states flared up again in 465 BC, when a helot revolt broke out in Sparta . The Spartans summoned forces from all of their allies, including Athens, to help them suppress the revolt . Athens sent out a sizable contingent (4,000 hoplites), but upon its arrival, this force was dismissed by the Spartans, while those of all the other allies were permitted to remain . According to Thucydides, the Spartans acted in this way out of fear that the Athenians would switch sides and support the helots; the offended Athenians repudiated their alliance with Sparta . When the rebellious helots were finally forced to surrender and permitted to evacuate the state, the Athenians settled them at the strategic city of Naupactus on the Corinthian Gulf . </P>

Which of the following played a critical role in the change in roman military strategy after 400 bce