The Peloponnesian War started when Sparta the leader of the Peloponnesian league and the largest land power in the region started to become concerned with the rise of Athens powers. Athens was a power in their own right; they were the largest sea power and the leader of the Delian league. Neither Sparta, nor Athens could afford to accept supremacy from the other country. Power can be a dangerous thing, those who have it don’t like letting it go, and those who don’t have it will do anything to get it. Before the Sicilian expedition the Athenians interests in western trade had been growing, but Pericles were more concerned in consolidating allies closer to home. When he died in 429 BC people’s attitudes towards the west changed, it had become
