History of the Peloponnesian War

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.

And he had become hostile because the Athenians had made an alliance with his brother Philip and with Derdas, who were making common cause against himself.

Alarmed at this he kept sending envoys to Lacedaemon, trying to bring about a war between Athens and the Peloponnesians. He sought also to win over the Corinthians, with a view to the revolt of Potidaea;

and, furthermore, he made overtures to the Chalcidians of Thrace and the Bottiaeans to join in the revolt, thinking that if he had as allies these countries, which bordered on his own, it would be easier, in conjunction with them, to carry on the war.