Lack of political unity within Greece resulted in frequent conflict between Greek states. The most devastating intra-Greek war was the Peloponnesian War (431–404 BC), won by Sparta and marking the demise of the Athenian Empire as the leading power in ancient Greece. Both Athens and Sparta were later overshadowed by Thebes and eventually Macedon, with the latter uniting most of the city-states of the Greek hinterland in the League of Corinth (also known as the Hellenic League or Greek League) under the control of Philip II. Despite this development, the Greek world remained largely fragmented and would not be united under a single power until the Roman years.
Extract what happened to Athens in the Peloponnesian War
Athens lost the Peloponnesian war leading to the demise of the Athenian Empire