The Delian League was not the only alliance in Greece. After the Persian Wars, many cities in the southern Greece, including Sparta, banded together as well. This aliance was called the Peoponnesian League after the peninsula on which the cities were located.
The growth of Athenian power worried many cities in he Peloponnes League. Finally, to stop Athens's growth, Sparta declared war.
This declaration of war began the Peloponnesian War, a war between Athens and Sparta that threatened to tear all of Greece apart. In 431 BC the Spartan army marched north to Athens. They surrounded the city, waiting for the Athenians to come out and fight. But the Athenias stayed in the city, hoping that the Spartans would leave. Instead, the Spartans began to burn the crops in the fields around Athens. They hoped that Athens would run out of food and be forced to surrender.
The Spartans were in surprise. The Athenian navy escorted merchant ships to Athens, bringing plenty of food to the city. The navy also attacked Sparta's allies, forcing Spartans to send troops to defend other Greek cities. At the same time, though, diseases swept through Athen's, killing thousands. For 10 years neither side could gain adventure over the other. Eventually, they agreed to a truce. Athens kept its empire, and the Spartans went home.