Peloponnesian War Ended The Greek Empire – Wikipedia

The Sicilian disaster prompted the third phase of the war (413–404 BC), named the Decelean War, or the Ionian War, when the Persian Empire supported Sparta in order to recover the suzerainty of the Greek cities of Asia Minor, incorporated into the Delian League at the end of the Persian Wars. With Persian money, Sparta built a massive fleet under the leadership of Lysander, who won a streak of decisive victories in the Aegean Sea, notably at Aegospotamos in 405 BC. Athens capitulated the following year and lost all its empire; Lysander imposed puppet oligarchies on the former members of the Delian League, including Athens, where the regime was known as the Thirty Tyrants

The Peloponnesian War reshaped the ancient Greek world. On the level of international relations, Athens, the strongest city-state in Greece prior to the war’s beginning, was reduced to a state of near-complete subjection, while Sparta became established as the leading power of Greece. The economic costs of the war were felt all across Greece; poverty became widespread in the Peloponnese, while Athens was completely devastated, and never regained its pre-war prosperity.[2][3] The war also wrought subtler changes to Greek society; the conflict between democratic Athens and oligarchic Sparta, each of which supported friendly political factions within other states, made war a common occurrence in the Greek world. Ancient Greek warfare, meanwhile, originally a limited and formalized form of conflict, was transformed into an all-out struggle between city-states, complete with atrocities on a large scale. Shattering religious and cultural taboos, devastating vast swathes of countryside, and destroying whole cities, the Peloponnesian War marked the dramatic end to the fifth century BC and the golden age of Greece.[4]

Peloponnesian War – Wikipedia