In the last lecture we witnessed the Persian Wars. We saw that the Greeks ultimately defeated the Persians as they advanced into Greece twice during the early fifth century. We also saw that these invasions resulted in three chief shifts in Greece. First, the Greek poleis were temporarily unified in the Delian League. Second, we saw that Athens took advantage of the Delian League to expand their own empire. And third, Sparta challenged Athenian authority and formed the Peloponnesian League. All of this took place between the 480s and 440s. By the 430s, the divisions in Greece were so strong that civil war had become inevitable. This civil war is called the Peloponnesian War and it shall be the focus of this lecture. This was the most pivotal war in Ancient Greek history because it will set the Greek poleis up for failure and invasion from Macedonia.