Athens was overconfident when it entered the war, imagining the combination of the money it collected from its empire, the strength of its walls, and the dominance of its navy would see it through. The Persians swung the balance, donating money to the Peloponnesian League to buy and man a fleet to match the Athenian one. With it's fleet defeated, its sea food route closed, and city besieged, Athens was starved out.