Leadup to the Peloponnesian War

The Athenian Empire

I will now take my own advice and attempt to explain the Peloponnesian War only with the help of maps.*  As the linked map makes clear, the Athenian Empire was very much a naval empire.  It consisted of the Greek islands and coastal Greek colonies surrounding the Aegean Sea, extending as far east as Byzantium.**  It included mostly Ionian colonies liberated from the Persians and did not cover most of Greece proper, or inland areas, nor did it extend to the western Greek colonies.  Athens did not actually conquer and subjugate these areas unless they revolted against its rule, but it did collect tribute and interfere with their sovereignty in ways that gave offense and bred rebellion.

Thucydides was the first historian to distinguish between the underlying and immediate causes of a war.  He describes the underlying cause of the war as the growing power of the Athenian Empire and Sparta's fear of it.  He also strongly implies that the other cause was the allies' resentment of Athenian domination, their eagerness to shake off the Athenian yoke, and Sparta as the main counterweight to turn to.  Yet Sparta, lacking serious naval power, had little assistance to offer these other city-states.

The Athenian Empire and Peloponnesian League had made a thirty-year truce in 446/445 B.C.  This truce did not actually mean peace for Greece as a whole.  It only meant that the two major powers were not at war with each other.  There were numerous other wars by smaller city states, and the great powers often intervened or fought their own wars.  They simply refrained from war with each other, rather as the US and Soviet Union never exchanged a shot during the Cold War, yet managed to fight many wars by proxy.

It was the escalation of these proxy wars that was the immediate cause of the war between the great powers.  None would have had the logic of bringing about war between the major Greek powers if it had not been for the underlying balance-of-power issue.   The main naval powers besides Athens were Corinth (moderate oligarchy, major commercial rival of Athens and member of the Peloponnesian League) and Corcyra (democracy, island on the western side of the Greek peninsula, modern Corfu, and colony of Corinth).  These two powers between them founded the colony of Epidamnos, far north on the western side of the Greek peninsula.  Around 435 B.C., civil war broke out between the democratic and oligarchic factions. Corinth, though an oligarchy, intervened on the democratic side and Corcyra, though a democracy, intervened on the oligarchic side, proving once again that ideology takes a second place to self-interest.  Corinth and Corcyra were soon at war with each other.  Both sides approached Athens, Corcyra to appeal for help, and Corinth to convince Athens to stay out.  The Cornithians argued that it was a member of the Peloponnesian League, Athens had a truce with the Peloponnesian League, and that to side with Corcyra would therefore breach the treaty.  Athens, fearing the naval might of Corinth if it were to conquer Corcyra, made a defensive pact with Corcyra that, unsurprisingly, soon escalated into war with Corinth.  This must have looked alarming to the Spartan because it was the first time that Athens had extended its power to the western side of the Greek peninsula, and suggested further imperial ambitions.

Flash Points in the Lead-up to War

Conflict with Corinth soon led to conflict with another Corinthian colony, Potidea.  Potidea was in an area on the east side of Greece know as the Chalcidice, on the north side of the Aegean, a city on a long peninsula and a part of the Athenian Empire.  In 432 B.C. the Athenians, fearing that Potidea would side with its mother country, began issuing a series of outrageous ultimatums to Potidea, demanding that it disarm and sever relations with Corinth.  The Potideans revolted after receiving assurance of Corinthian naval support and a Spartan promise to invade Athens if it attacked (recall that Sparta, as a land power, had little direct assistance to offer).  Athens proceeded to besiege Potidea.

As the attached map makes clear, these two events took place on opposite sides of the Greek peninsula and were not directly related, except that both involved conflict between Athens and Corinth, an ally of Sparta.  But Athens' alliance with Corcyra must have looked like an alarming imperial design on the west, and its behavior toward Potidea like little more than wanton aggression. Corinth.  Furthermore, Athens had a trade embargo on Spartan ally Megara (a factor most modern historians consider a good deal more important than Thucydides gives credit for).  Corinth began agitating the Peloponnesian League for war.  Athens and Sparta soon began exchanging the sort of dueling ultimatums that countries exchange when the want to go to war but each wants the other to look like the aggressor.

Yet interestingly enough, it was not an imperial act by Athens that finally convinced the Spartans to go to war, but a completely defensive and justified one.  The nearest major power to Athens was Thebes, an oligarchy and Spartan ally.  Only about eight miles from Thebes lay the small town of Platea, a democracy that had aligned itself with Athens to seek protection from Theban hegemony. Athens regarded Platea as its most cherished ally because Platea was the only city to come to Athens' assistance at the Battle of Marathon.  One dark night in 432 B.C., Platean oligarchs invited about 300 Theban troops into Platea to bring them into alliance with Thebes.  The oligarchs wanted the Thebans to kill the leaders of the democratic faction and take over by force.  Instead, the Thebans called the Platean assembly into session and tried to persuade them.  That Plateans were at first intimidated into submission but, realizing the Theban force was small, attacked.  Women and children joined the attack by climbing up on the rooftops and pelting them with rocks and tiles.  Some of the Thebans escaped, some were killed, and some were captured.  That Plateans persuaded any forces outside the walls not to attack the rural dwellers by threatening to kill the capture forces.  They sent to Athens for instructions on what to do.  The Athenians warned the Plateans not to harm their captives, but the Plateans had already killed them.***  The Athenians presumably knew that this meant certain war with Thebes, and apparently doubted their ability to protect their ally because they evacuated most of the non-combatants, leaving only a garrison of 400 men, backed by 80 Athenians, and 110 women to provide support functions such as cooking.

This episode was apparently considered by both sides as the final breach of the truce and grounds for war.  War was formally joined in 431 B.C. It continued for ten years, ending in a short-lived peace in 421 B.C.  My next much of those next ten years as I can fit in.

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*This is good advice for any war.  There is a reason why military men are so fond of maps.
**There were also Greek colonies east of Byzantium, surrounding the Black Sea, but Athenian hegemony did not extend that far.
***Presumably the Plateans lacked facilities for keeping so many prisoners, while the Athenians had them.