Thucydides’ Ignored Lesson


Thucydides’ history of the Peloponnesian War (431-404 BC) holds crucial lessons about the nature of great power war, beyond the much-vaunted cause and effect construction of the outbreak of Athens-Sparta hostilities known as the “Thucydides Trap.” The purported inherent cause — a resident power’s fear and desire to crush ascendant competition — of the epic clash between the two dominant city-states of ancient Greece is more ambiguous than Trap thesis proponents maintain. More certain and instructive is the enervating dynamic of such titanic conflict: Great power wars conducted by similar-sized military forces, equipped with similar weapons, and applying similar warfighting methods will lead to a protracted stalemate, only to be broken when one side collapses from human and material exhaustion.

The narrative of the war between the Athenian Empire and Sparta and her allies as presented by Thucydides (and Xenophon) shows that great power wars often are not won by one (or even a number of) decisive battles but rather by long and drawn out attrition warfare after initial strategies by both sides to force a decisive result have failed. Furthermore, the history of the Peloponnesian War teaches that victory in such type of a war comes at enormous cost to both sides, often blurring the binary distinction between victor and loser.

Hubris and Military Power

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The war between Athens and Sparta was a war of choice rather than necessity, sparked by imperial hubris on the one hand and chance, a sequence of events unintentionally brought about by hapless humans, on the other hand. Hubris and chance, as so often throughout history, played a mutually reinforcing role in unleashing organized bloodshed.

In the case of Athens and Sparta, hubris, or dangerous overconfidence, derived from the leading role both city-states played in defeating Persia during the Greco-Persian Wars (499-449 BC) and the creation of defensive alliances, the Delian League led by Athens (which would turn into the Athenian Empire) and the reformed Peloponnesian League under the leadership of Sparta. Both leagues were ostensibly formed to defend against a Persian invasion. Yet in reality they were instruments for the two leading city-states to project hegemony in their respective spheres of influence. Nonetheless, contrary to popular belief, neither side was seeking to dominate all of Greece.

Among other, more systemic reasons, the war was directly caused by Athens provoking Corinth, a Spartan ally. (Provocations included ostensibly neutral Athenians intervening in a battle against Corinthian forces and trying to force a Corinthian colony to become submissive to the Athenian Empire.) In turn, Corinth asked Sparta to stand by its side and declare war on Athens. Sparta eventually consented due to a fear that it would lose credibility within the Peloponnesian League should it not meet the demands of a key ally (Sparta needed its allies to prevent the helot population from revolting). Soon thereafter, Athens also voted for war since it refused to yield to rather modest Spartan demands, with Athens’ first citizen Pericles clinging to the old adage that appeasement makes the aggressor only more aggressive.

Thus the war began. Both alliances were able to field substantial military forces at the outset of hostilities. The Athenian Empire, primarily a naval power, commanded a fleet of around 400 warships (“triremes”), whereas Sparta, a land power, and its allies boasted the finest hoplite fighting force in the Greek world.

The alliances’ relative strengths dictated their respective warfighting strategies. The Athenians would hole up behind their long walls connecting Athens with its ports of Piraeus and Phalerum, raid the Peloponnesian coastline, and avoid battle while harassing the Spartan Army from outposts sustainable from the sea and acting as forward bases for launching sudden strikes until Sparta grew tired of war and would concede Athenian parity. Sparta’s plan was simple: Invade Attica, devastate Athenian crops, and force the Athenians into battle, which the latter would almost certainly lose.

Both sides expected a relatively short conflict. The Athenian leader Pericles estimated that Sparta would grow tired after one or two campaign seasons and enter negotiations (overall, he calculated that Athens had financial resources for a three-year war), whereas Sparta believed that Athens would sue for peace as soon as its citizens saw Attica’s farmland devastated. (More astute Spartan strategists called for the construction of a 500-ship fleet to destroy the Athenian imperial fleet — the ultimate guarantor of Athenian power.)

No Easy Victory

Yet the war between the two alliance blocs would turn out to be one of the most brutal and devastating conflicts in Greek history. It was the first time that a war was not just fought in the spring and summer but throughout the entire year, which meant that citizen soldiers and sailors were not able to return home every year to harvest their lands. The conflict also saw widespread atrocities including the destruction of entire cities, the wholesale slaughter of civilians and their enslavement (e.g., during the attack on Melos), as well as civil strife (e.g., in the city-state of Corcyra).

The war went on inconclusively for years as casualties mounted. Following the battle of Amphipolis in 422 BC, both sides agreed to an armistice that lasted six years. Hostilities resumed and Athens eventually embarked on an expedition to take the Greek city-state of Syracuse in Sicily, suffering one of its most disastrous defeats during the entire war. The fortunes of war went back and forth for several more years, slowly depleting the manpower and financial resources of both sides. Eventually, the Spartans, with the help of the Persians, succeeded in destroying the Athenian imperial fleet in 405 BC, which led to the capitulation of an exhausted and starved Athens the following year.

Why did the war last so long and why was it so destructive?

One of the principal reasons was that both sides fought with similar equipment and used similar tactics. The bulk of the Athenian and Spartan armies consisted of heavily armored infantry armed with round shields and spears fighting in a tight battle formation known as the phalanx. This phalanx was usually supported by lighter infantry (“psiloi”), missile troops of some sort (e.g., “peltasts”), and occasionally cavalry. Battles during the Peloponnesian War were rare, however, as Athens favored small actions, whereas Sparta sought decisive hoplite battles. Nevertheless, when hoplite forces did clash, the aftermath could be as devastating (or often more so) in terms of human destruction than the battle itself. Athens and its allies lost around 40,000 people following the final Syracusan victory in Sicily in September 413 BC.

Throughout the war, both Athens and Sparta also employed similar strategies of devastation to force the defender out of fortified cities to avoid long, drawn-out sieges. That is, invasions of enemy lands usually took place immediately before the harvesting season to wreak maximum damage upon agricultural lands. If the devastation did not succeed in convincing defenders to fight a hoplite battle (as was the case with the Athenians during the first ten years of the war), the invader could lay siege to a city. However, the Greeks during the Peloponnesian War lacked the technology and manpower to construct effective siege equipment (perhaps with the exceptions of the Spartans, who succeeded in building a siege-mound and taking the city of Plataea early in the war). As a result, the attacker usually had to starve out the defenders, which could take months or years and often ended with the enslavement of the city’s population if not death.

Moreover, while Sparta and its allies fielded a formidable hoplite fighting force and Athens uncontestably ruled the waves at the outset of the conflict, the long war led to both sides adapting and incorporating skills and innovations from the other side. For example, Sparta fielded a formidable navy toward the end of the conflict, and Athens gradually adapted its infantry force to defeat Spartan troops on land. This gradual leveling of combat capabilities further contributed to the prolonging of the conflict, as engagements were seldom decisive unless major blunders by military commanders occurred. A case in point is that the last major battle of the war, fought in 405 BC at Aegospotami and which eventually resulted in the capitulation of Athens, owed its decisive nature not to the superior skills of the Spartans, according to most accounts, but to surprise and a Spartan sneak attack.


The lesson of the Peloponnesian War for policymakers who are mulling the use of military force to press their national interests is obvious. Despite examples throughout history of quick and complete victories in great power confrontations (e.g. the Wars of German Unification), bloody and exhausting wars of attrition are the more likely outcome — especially when both sides enjoy rough conventional military parity including fielding similar armies, navies, and deploying similar military technologies.

This is further accentuated by the existence of alliances such as the Hellenic Peloponnesian and Delian Leagues, which makes it even harder to deal the enemy a Clausewitzean knockout blow in a decisive battle. Indeed, battles under such circumstances, as the clash between Athens and Sparta illustrates, only accelerate underlying rates of human and material attrition. The famed Spartan hoplite phalanx gradually declined in size and Athens imperial fleet progressively lost its best rowers (the “thetes” — Athens poorest citizens) as the war went on, irrespective of victories won by both sides.

Furthermore, long, drawn out wars fought alongside allies often blur the line between victor and loser. Similar to Great Britain and France, which both lost their empires following World War II, Sparta was not able to reap the fruits of victory in the Peloponnesian War for very long. Athens eventually rebuilt its fleet and long walls and would continue to play a decisive role in Greek culture and politics for almost two centuries, whereas Spartan power would eventually be dealt a death blow, from which it would never recover, by Thebes in 371 BC.

The palpable lesson to take away from the Peloponnesian War is as simple as it is appears naïve. Wars of choice between great powers that have access to the same military technologies, field similar armed forces, and are embedded in rigid alliance structures, should be avoided — unless one is prepared to endure the 21st century political equivalent of the devastating Athenian plague. This lesson is even more compelling today given the existence of arsenals of weapons of mass destruction.

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