The Origins of the Peloponnesian War

Robert Joseph, Dickson College 2009

The fear between Athens and Sparta was the long-term cause of the Peloponnesian War. Athens’ reliance on its naval superiority was a short-term cause, as this caused it to risk provocation in the Corcyra affair. Sparta declared war on Athens to protect Corinth in the short term, and to prevent the long-term growth of Athens, which they feared would weaken the Spartan Alliance. At the outbreak of the war, this fear was so strong, that Sparta was determined to go to war with or without a reasonable pretext. Thus, the most important cause of the Peloponnesian war was Sparta’s fear of Athens, and their failure to contain it.

The long-term cause of the Peloponnesian war was fear between Sparta and Athens, which made any attempt at peace unstable. The Athenian Empire, which grew out of the Delian League[1] , first fought against the Spartan Alliance in the First Peloponnesian War from 460-446BC. The war was concluded with the Thirty Years Peace of 446/5BC, whereby Sparta officially recognised the Athenian Empire[2] . The treaty forbade each power’s allies from warring with each other or switching sides. Since it essentially encouraged the status quo, it was obvious both sides desired peace as was shown in 440BC, when the Samians revolted against Athens, with Persian support. Several other revolts sparked around the empire, and Athens was in a vulnerable position. However, a meeting of the Peloponnesian League, led by Sparta, voted against aiding the Samians, thus showing their desire to maintain the peace. Nevertheless, peace requires not only restraint, but trust. So long as each side had the capacity to damage the other, there would always be suspicion and the peace would remain unstable. Sparta was constantly alert to the threat of an Athenian-assisted rebellion by the Helots, the conquered, serving-class of Peloponnese. This was evident when, during a Helot revolt in 464 BC, Sparta rejected Athenian aid, out of fear Athens would join or further incite the rebellion. Now, Athens’ land forces were always inferior to Sparta’s. Furthermore, there was always the risk of Sparta inciting their colonies to revolt, which would cripple Athens’ main sources of income. Thucydides writes that in 432BC Sparta told their allies

We also have other ways of carrying on the war, such as revolt of their allies, the surest method of depriving them of their revenues, which are the source of their strength…[3]

It was probably out of fear of this eventuality, that Athens amassed their huge reserve fund of 6000 talents[4] . Athens and Sparta each feared their weaknesses being exploited by the other; since the peace required these fears to be constantly contained, it was inherently unstable, requiring only a small action for the suspicion to turn into war.

The Corcyra affair escalated into a short-term cause for the Peloponnesian war, because of Athens’ long-term dependence on their naval power. Corcyra, a naval power and one of the few neutral Greek city states left, had become embroiled in a conflict with its founding state Corinth, a member of the Spartan Alliance. Facing the threat of a Corinthian invasion, Corcyra sent envoys to Athens in 433 BC, offering an alliance. The envoys clearly relied on Athens’ naval interests to induce them to enter the war, saying

Remember that there are but three considerable naval powers in Hellas, Athens, Corcyra and Corinth, and that if you allow two of these three to become one, and Corinth to secure us for herself, you will have to hold the sea against the united fleets of Corcyra and Peloponnese. But if you receive us, you will have our ships to reinforce you in the struggle.[5]

Pericles, the leading Athenian statesman, saw naval power as the key advantage Athens held over Sparta, once saying

...our naval skill is of more use to us for service on land, than their military skill is to them at service at sea.
His strategy for defeating Sparta relied on

…our sailing into their country, and raising fortifications there, and making reprisals with our powerful fleet.[7]

If Corcyra’s navy joined Corinth, it could challenge Athens’ naval superiority, the only advantage they had in a potential war with Sparta. Athens was thus compelled to agree to Corcyra’s appeal. However, while this action did not violate the treaty[8] , it gave Athens an aggressive appearance. Attempting to nullify this impression, and show their desire for peace, they specified that it “…be a defensive, not an offensive, alliance”[9] . They demonstrated this by sending 30 ships to help Corcyra at the Battle of Sybota in 433BC[10] . The Corinthians won, but withdrew the next day after the arrival of more Athenian ships. The Athenians did not pursue the retreat. Soon after, Potidaea, a former colony of Corinth, revolted with Corinthian support against Athens, who immediately besieged it. Thus, the Corcyra affair intensified into the immediate cause of the war because Athens’ entire defence strategy relied on their naval superiority.

Sparta declared war because in the short-term they were reluctant to see Corinth defeated, and in the long-term they feared further Athenian growth in power. Determined to continue the war against Athens, Corinth appealed for Sparta to declare war on Athens. Before the vote, a Spartan ephor, Sthenelaidas, urged his country to “neither allow the further aggrandizement of Athens, nor betray our allies to ruin.”[11] . The Spartans subsequently voted to join Corinth, although the vote was close enough that they resorted to counting over the traditional voice acclamation[12] . Clearly, the advocates for peace that were successful during the Samian revolt, had lost the support of those Spartans who, already suspicious of Athenian intentions, saw their fears justified in the wake of Athens’ recent demonstration of power. They would also have realised that if Corinth were defeated, Sparta would have lost their foremost naval ally who would be crucial in a war with Athens. Sparta could lose the support of their Peloponnesian allies, if they offered no resistance to Athens’ attempt to defeat one of them. This sentiment was expressed in a Spartan address to their allies:

…unless as a body and as individual nationalities and individual cities we make a unanimous stand against her, she will easily conquer us divided and in detail.[13]

Sparta declared war not only as an immediate response to Athens’ activities, but out of a long-term fear of Athens gradually weakening the Spartan Alliance.

Athens’ refusal to make concessions to Sparta, and Sparta’s determination to accept no less, made the Peloponnesian war unavoidable, despite the flurry of diplomatic activity. During the year that elapsed between Sparta’s declaration of war and their first invasion of Attica, Sparta sent embassies to Athens. One of these offered a proposal to prevent war. Thucydides writes that

Above all, it gave her most distinctively to understand that war might be prevented by the revocation of the Megarian decree…[14]

The Megarian decree was an economic sanction that Athens imposed on the Megarians, prohibiting them from trading with Athenian ports[15] . Despite it being a minor policy, the Athenians, especially Pericles, were adamant that it be maintained, because they feared that a concession would not only constitute a loss of pride, but would be seen as a sign of weakness, and would be exploited by Sparta. Pericles told the Athenians

If you give way, you will instantly have to meet some greater demand, as having been frightened into obedience in the first instance; but a firm refusal will make them clearly understand that they must treat you more as equals.[16]

So while Athens was eager to avoid a war, they would grant no concessions to Sparta. To press this point, Pericles responded with a counter-proposal, saying

…we will allow Megara the use of our market and harbours when the Lacedaemonians [Spartans] suspend their alien acts in favour of us and our allies.[17]

The historian, G.E.M. de Ste. Croix interprets this as a request for Sparta to cease the expulsion of the Athenians and their allies from Spartan territory[18] . Sparta refused the offer, preferring war. If the Spartans had truly wished to avoid a war, they would have accepted this even-sided offer, but it seems that they would only be content with the defeat of Athens, or a concession that acknowledged Sparta’s superiority. Thus, their embassies were not a genuine attempt at peace. Thucydides believed their diplomacy was merely an attempt to justify their actions. He wrote that Sparta sent

…embassies to Athens charged with complaints, in order to obtain as good a pretext for war as possible…[19]

This is a reasonable interpretation when it is remembered that it was Sparta, not Athens, who would be breaking the Thirty Years Peace[20] . Thus, Thucydides may have been right when he famously said

The growth of the power of Athens, and the alarm this inspired in Lacedaemon, made war inevitable.[21]

The only acceptable terms for Sparta, were completely unacceptable for Athens. Sparta’s fear of Athens had grown to the point where war was inevitable, since they were determined to go to war, with or without a reasonable pretext.

The Peloponnesian war was caused in the long-term by Athens and Sparta fearing the military powers of each other. The short-term catalyst was Athens' allying with Corcyra to retain the naval advantage they relied on to protect them from Sparta. Sparta’s declaration of war on Athens was a short-term way to save Corinth, and a long-term strategy to halt Athens’ growth in power, which Sparta feared. Sparta’s long-term fear of Athens had grown to the point where they were determined to break the treaty and conquer Athens, even when they realised their pretext was dubious. Of the many factors that caused the Peloponnesian war, the most important was Sparta’s fear of Athens, which made them determined to attain the latter’s defeat.


AAC staff 1998, The Peloponnesian War, viewed July 29th, 2009, <>
Kagan, Donald, The Peloponnesian War, HarperCollins, USA, 2003
Plutarch 75 AD, Pericles, viewed August 22nd, 2009, <>
Ste. Croix, G.E.M. de, The Origins of the Peloponnesian War, Duckworth, Great Britain, 1972
Thucydides c.410 BC, The Peloponnesian War, University of Wisconsin, USA, 1982
  1. ^ Following the Battle of Plataea in 479BC, Athens continued the expulsion of the Persians without Spartan help, eventually forming the Delian League.
  2. ^ Kagan 2003, p. 19
  3. ^ Thucydides, I 122
  4. ^ Thucydides, II 13
  5. ^ Thucydides, I 36
  6. ^ Thucydides, I 142
  7. ^ Thucydides, I 141
  8. ^ Ste. Croix 1972, p. 71
  9. ^ Thucydides, I 44
  10. ^ Kagan 2003, p. 36
  11. ^ Thucydides, I 86
  12. ^ Thucydides, I 87
  13. ^ Thucydides I, 122
  14. ^ Thucydides, I 139
  15. ^ Ste. Croix 1972, p. 253
  16. ^ Thucydides, I 140
  17. ^ Thucydides, I 144
  18. ^ Ste. Croix 1972, p. 289
  19. ^ Thucydides, I 126
  20. ^ Ste. Croix 1972, p. 257
  21. ^ Thucydides, I 23