Which led to the decline of the Athenian empire?

The decline of the Athenian empire was primarily due to the devastating impact of the Peloponnesian War (431-404 BCE), fought against Sparta and its allies. A series of military defeats, coupled with economic strain and internal strife, weakened Athens significantly. Additionally, the plague that struck the city in 430 BCE decimated its population and military strength. Ultimately, the empire's reliance on naval power and failure to secure lasting alliances contributed to its downfall.