The PELOPONNESIAN LEAGUE was anti-Athens alliance led by Sparta that included Thebes, Corinth, and Megara. Tensions between Athens and Corinth led to the first Peloponnesian war from 460-446 BC. due to a devastating earthquake and helot revolt, Sparta was mostly absent from this part of the conflict. This shorter war ended with a truce that only lasted 15 tears before fightiing began again in 431 Bc- this time with Sparta leading the anti- Athens forces.
Athens stretegy was to avoid fighting the Spartan army but, instead they focused on using the superior Athenian navy to attack sparta and its allies from the sea. The Athenians had more money and more men than Sparta so they could fight a long war.