In this lecture, Professor Donald Kagan examines the developments that took place after the Greek victory over the Persians in 479 BC. He argues that even after the Greek victories, there was great fear amongst the Greeks that the Persians would return to seek revenge. For this reason, many of the Greek poleis, especially the islands, looked to Athens to lead this league, which later became the Delian League. Athens, according to Professor Kagan, accepted this responsibility, since it too feared a Persian invasion, but Sparta was content to retreat into the Peloponesus. Finally, Professor Kagan intimates that this league would eventually turn into the Athenian empire.