Final answer:
Sparta's fear of Athens during the Golden Age intensified due to Athens's accumulation of wealth, power, and its influential democratic lifestyle, contrasting sharply with Sparta's oligarchic system, concluding with the Peloponnesian War and Spartan victory supported by Persia.
Step-by-step explanation:
During the Golden Age, Sparta's fear of Athens grew more intense primarily because of the wealth and power that Athens had accumulated. Athenian support of Corcyra against Corinth, which was an ally of Sparta, led to growing tensions, resulting in the outbreak of the Peloponnesian War in 431 BCE.
Furthermore, Athens's military successes, particularly at sea, and the establishment of a democratic way of life that contrasted with Spartan oligarchy and rigorous discipline, exacerbated Spartan fears. Events such as Athens's defeat in Sicily, and the subsequent Spartan victory with Persian support, emphasized the strategic threat that Athens represented to Sparta. The alliance between Sparta and Persia was especially significant, as Persia had been a former enemy, but it now supported Sparta's naval endeavors against Athenian dominance.