History of the Peloponnesian War
Thucydides
Thucydides, Vol. 1-4. Smith, Charles Foster, translator. London and Cambridge, MA: Heinemann and Harvard University Press, 1919-1923.
In this way, then, Corcyra had the advantage in the war with the Corinthians, and the ships of the Athenians withdrew from it. And this was the first ground which the Corinthians had for the war against the Athenians, because they had fought with the Corcyraeans against them in time of truce.
Immediately after this the following events also occurred, which caused differences between the Athenians and the Peloponnesians and led to the war.
While the Corinthians were devising how they should take vengeance on the Athenians, the latter, suspecting their enmity, required of the Potidaeans (who dwell on the isthmus of Pallene and are colonists of the Corinthians but tributary allies of the Athenians), to pull down their wall on the side of Pallene and give hostages, and, furthermore, to send away and not receive in the future the magistrates whom the Corinthians were accustomed to send every year. For they were afraid that the Potidaeans, persuaded by Perdiccas' and the Corinthians, would revolt and cause the rest of the allies in Thrace to revolt with them.
These precautions the Athenians took with regard to the Potidaeans immediately after the seafight at Corcyra;
for the Corinthians were now openly at variance with them, and Perdiccas son of Alexander, king of the Macedonians, who had before been an ally and friend, had now become hostile.