The History of the Grecian War (1.55.1-1.56.1)

The Corinthians in their way homeward took in Anactorium, a town seated in the mouth of the Gulf of Ambracia, by deceit (this town was common to them and to the Corcyraeans), and having put into it Corinthians only, departed and went home. Of the Corcyraeans, eight hundred that were servants they sold, and kept prisoners two hundred and fifty, whom they used with very much favour that they might be a means, at their return, to bring Corcyra into the power of the Corinthians, the greatest part of these being principal men of the city.

And thus was Corcyra delivered of the war of Corinth, and the Athenian galleys went from them. This was the first cause that the Corinthians had of war against the Athenians: namely, because they had taken part with the Corcyraeans in a battle by sea against the Corinthians with whom they were comprised in the same articles of peace.

Presently after this, it came to pass that other differences arose between the Peloponnesians and the Athenians to induce the war.