The Peleponnesian Wars broke out as a result of a power vacuum created in the Aegean basin after Persia was defeated in the Persian wars. Athens, which had a powerful navy, had attempted to occupy this power vacuum by creating the Delian League. It forced a number of city states to join, many against their will, and imposed exorbitant taxes for the league's upkeep. Those city states who attempted to leave the league were suppressed ruthlessly. Alarmed at the spreading influence of Athens, Sparta formed the Peleponnesian League. The first war broke out when Syracuse, a city state, attempted to leave the Delian League and join the Peleponnesian League. The first war lasted twenty seven years as Athens, a sea power, and Sparta, with a large land force, had difficulty fighting each other. The war ended with the Peace of Nicias in 421 B.C.E. The treaty called for a fifty years peace.
The second war broke out when Alcibiades, an Athenian leader, defected to Sparta. He and his men were accused of having emasculated statues of Hermes throughout Athens, a grave insult. The second war ended with the defeat of Athens and Sparta in control of the Greek mainland.