The Epidamnus incident
The truce of Euboea entered into between Athens and Sparta after Athens had subduded that island was still in place albeit shakey as it was.
The city of Epidamnus was a colony or Corcyra whos inhabitants were from Corinth. The once powerful city fell into ruin because of faction and constant incursions by barbarians.
Because of this constant strife, nobles were expelled. These exiles joined forces with the barbarians in attacking the city. Epidamnus in desperation asked Corcyra for help, but they would not offer any assitance. In anguish they then went to Delphi to ask the gods wether they should give their city to Corinth, Delphi replyed that they should.
The city of Corinth offered Epidamnus help, not because they saw their citizens as having originally come from Corinth, but more because friction between Corinth and Corcyra already existed, and this seemed like a good way of sticking it to them. Corinth sent citizens and soliders to help defend the city.
Corcyra would have none of this and demanded that Corinth evacuate. Talks took place between the two and Corcyra brought in a contingent from Sparta to aid their ambassadors in negotiations. This is because Sparta was trying to keep the status quo at this stage and didn't want allies in the Peloponnese at war with each other. Talks between the two failed and Corcyra joined the barbarians in besiging the city, Sparta would not allie with either city.
Corinth immediatley organised their navel fleet for the defence of Epidamnus.
'The history of the Peloponnesian Wars' by Thucydidies (written c431 B.C),translated by Richard Crawley 1910.
Epidamnus: founded c. 625
• Corcyra establishes the city through a Corinthian named Phalius who serves as founder with other Corinthians amoung the settlers. (1.24.2) so it is a joint colony of Corcyra and Corinth
• founded as a port of call on the Adriatic coast and a focus of trade from Illyria
-- trade first monopolized for the benefit of the ruling oligarchic class
• industrial pursuits restricted to industrial slaves
• 435 BC: commons gained control and expelled oligarchy
-- seiged by ousted oligarchs
-- Epidamnos applied to Corcyra for aid; she refused
-- applied to Corinth for help; Corinth supported democracy with new settlers
• shortly after 435 BC, Corcyrans recaptured city
• struggle over control of colony by Corcyra and Corinth was contributing factor to Peloponnesian War
Note 1: As the Corinthians learn of the seige, we find that the number of Greek cities involved greatly increases: Megara, pales on Cephallonia, Epidaurus, Hermione, Troizen, Leucas, Ambracia, Thebes and Elis all play a part.