Athens and Sparta, both powerful Greek city-states, had fought as allies in the Greco-Persian Wars between 499 and 449 B.C. In the wake of the Persian retreat, however, Athens grew more powerful and tensions rose, escalating into nearly three decades of war. Sparta emerged victorious, while the constant fighting left Athens bankrupt, exhausted and demoralized. Neither city-state regained the military strength they once had.
After heroic roles in the defeat of the Persians (480-479 B.C.), for the next half-century Athens and Sparta assumed preeminence among the city-states, and their rivalry slowly led to the long-expected showdown. Thucydides, a contemporary historian, believed that the war broke out because of Spartan fear of the rising power of Athens, whose empire and capital increasingly isolated less imaginative and less adventurous rivals. Both were unusually powerful, atypical–and antithetical–Greek states that could afford to ignore the old rules of infantry warfare. Supported by nearly 200,000 Helots (serfs) who worked the farms of Messenia and Laconia, the Spartans fielded professional hoplites, year-round infantry not subject to the normal restrictions that free agriculture placed on yeomanry in infantry battle.
Nor were the democratic Athenians comfortable with an artificial collision of oligarchical, armored farmers. In the wake of the Persian retreat (479 B.C.), Athens’s fleet increased. Nurtured on the tribute of vassal states in the Aegean, Athens did not mothball its triremes; instead, they became a “benign” police force of sorts for its Greek subject allies overseas. Like the Spartans, imperial Athens too saw little need to limit warfare to a single afternoon, or indeed, given the success of its evacuation before Xerxes and subsequent naval response, to risk at all its hoplites in defense of the farmland of Attica. The majority of its citizens were not infantrymen and increasingly saw the navy as the bulwark of radical democracy.
Abandoning its countryside to Spartan invaders (431-425 B.C.), Athens understandably refused pitched battle with the crack hoplites of the Peloponnesian and Theban alliance. The strategy of attrition adapted by the Athenian leader, Pericles, depended on increased importation of food and material into the port at Piraeus, all the while sending out Athens’s magnificent fleet to stabilize its maritime empire and to prevent Peloponnesian infiltrations, forgoing major land engagements at all costs. Sparta found its old strategy of ravaging cropland discomfortingly ineffective: its hoplites in Attica could neither draw the Athenian army out nor reduce the city economically. The Spartans’ best ally was the unforeseen outbreak of plague inside the cramped walls of Athens, which killed Pericles and nearly one quarter of the citizenry. With stalemate in Attica, both belligerents turned to a variety of secondary theaters throughout the Aegean world and Asia Minor, as Sparta tried to turn Athenian subjects, and Athens in turn sowed insurrection among the Helots.
In these latter proxy wars, Athens used hoplites in combined maritime operations, whereas Sparta and its allies in time developed a competent fleet: during the entire course of the Peloponnesian War there were not more than three or four hoplite battles of the old style. Instead, mercenaries, lightly armed skirmishers, sailors, and siege engineers filled that void. All were expensive. And–disastrous for both sides–all apparently were incapable of ending an engagement decisively through a day’s destruction or humiliation of an enemy’s forces in the field.
Strategy became prominent for the first time in Greek warfare, as the Athenians made mostly inconsequential probes in and around the Peloponnesus. Their greatest success was the occupation of Pylos off the coast of the Peloponnesus (425 B.C.), where Spartan defenders were taken hostage and the way was made clear for Helot runaways. The subsequent failure of Sparta to reduce Athens in the first decade of the war led to a brief peace (421 B.C.).
But soon the Athenians intervened in the Peloponnesus (418 B.C.) and attacked neutral states in the Aegean. The folly of that aggressive policy culminated in the disastrous expedition to Sicily (415-413 B.C.), where nearly forty thousand Athenian allies perished a thousand miles from Athens. Sparta now systematically garrisoned Attica with a permanent fort at Decelea (413-404 B.C.) to encourage desertions and local disruptions in commerce, all the while applying steady pressure to pry away tribute-paying Athenians and their allies in the Aegean, the lifeblood of the city’s capital and military reserves. Unable to replace the manpower losses from the plague and the disaster at Sicily, the Athenian army and navy were routinely now outnumbered by the combined alliance of Sparta, Thebes, and Syracuse. Persian subsidies to this Peloponnesus-led coalition for the first time surpassed the financial reserves of Athens. After the final Athenian sea defeat off Aegospotami, the Long Walls down to the Piraeus were razed, and a Spartan garrison occupied the city.
Nearly three decades of constant fighting left Athens bankrupt, exhausted, and demoralized. But Sparta and its allies were in no position to maintain an even harsher military hegemony over Greece. In the detritus of the Peloponnesian War, the agrarian fighting of the old polis was ended. Warfare now meant expansion of conflict onto a variety of costly and deadly new horizons, where past protocol meant little. The Greek genius was freed to apply capital, technology, and manpower to war without ethical restraint, but in the process the old idea of a city-state was lost.