The Pelopennesian War took place in the ancient Greek city-states of Athens and Sparta. Battles also took place in many neutral states in the Aegean as the war expanded throughout Greece. The Spartan forces attacked the Athenian mainland, whereas the Athenians used their superior navy to attack the Pelopennesian peninsula.
Sparta and Athens were allies against the Persian empire. When they successfully drove the Persians back, Athens grew more powerful and sparked Spartan unease. The resulting Pelopennesian War lasted over 30 years and decimated the Athenian economy and weakened the Spartan forces greatly. As the Pelopennesian War expanded over much of Greece, it changed the way wars were fought at the time. Previously, wars had been relegated to a single afternoon.