Why did Sparta feel threatened by Athens during the 400 B.C.?

Sparta felt threatened by Athens in the 400s B.C. due to Athens' growing power, wealth, and influence, particularly following its leadership in the Delian League. The Athenian empire's democratic government contrasted sharply with Sparta's oligarchic military state, leading to ideological tensions. Additionally, Athens' naval superiority allowed it to challenge Spartan dominance on land and sea, escalating fears of Athenian expansionism and destabilizing the balance of power in Greece. This rivalry ultimately contributed to the outbreak of the Peloponnesian War.