Answer:
The wealth, prestige, policies, and power of Athens caused resentment among other city-states. A plague that killed many Athenians helped Sparta defeat Athens. The Peloponnesian War weakened all of the Greek city-states for 50 years.
The primary causes were that Sparta feared of the growing power and influence of the Athenian Empire. The Peloponnesian war began after the Persian Wars ended in 449 BCE. ... This disagreement led to friction and eventually outright war. Additionally, Athens and its ambitions caused increasing instability in Greece.