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====How did Athens growing power threaten Sparta?====

The origins of the Peloponnesian War lay in Greece's victory over the Persian Empire. The Greeks had combined under the leadership of Sparta and Athens to defeat the Persians, then the most powerful empire in Asia. In the aftermath of the Persian Wars, the Greeks were unable to maintain their unity. Cultural and ethnic differences were driving the Greek world apart. People’s first loyalty was often to their Polis or local city.