History of the Peloponnesian War

Such were the words of the Corinthians.When the Athenians had heard both out, two assemblies were held. In the first there was a manifest disposition to listen to the representations of Corinth; in the second, public feeling had changed, and an alliance with Corcyra was decided on, with certain reservations. It was to be a defensive, not an offensive alliance. It did not involve a breach of the treaty with Peloponnese: Athens could not be required to join Corcyra in any attack upon Corinth. But each of the contracting parties had a right to the other's assistance against invasion, whether of his own territory, or that of an ally.

For it began now to be felt that the coming of the Peloponnesian war was only a question of time, and no one was willing to see a naval power of such magnitude as Corcyra sacrificed to Corinth; though if they could let them weaken each other by mutual conflict, it would be no bad preparation for the struggle which Athens might one day have to wage with Corinth and the other naval powers.

At the same time the island seemed to lie conveniently on the coasting passage to Italy and Sicily.