score:11
Edit: I think I have to revise quite a bit. One thing is that the Peloponnesian Wars went through various stages which themselves got different titles (Ionian, Corinthian, etc).
As a result the poster on Yahoo Answers may be quite right. In the Ionian War, which crushed Athens, the Persians provided the gold for the Spartan Fleet.
In the Corinthian War, which pitted Sparta against former allies, Persia turned around and financed the other side.
Initially the Great King, Artaxerxes II, funded this anti-Spartan alliance, 49 because the Spartans had abandoned the treaty which they had struck with him during the Ionian War.
Instead of letting him levy phoros on Ionia’s Greeks the Spartans were now fighting him for control of them. Athens used Persia’s gold to rebuild its fortifications and its fleet.
Which Persia didn't like one bit, so they changed tack again:
These Athenian actions were manifestly at Persia’s expense. By the early 380s Athens was even backing revolts against the Persian Empire in Cyprus and Egypt. Artaxerxes II thus realised that by helping Athens to fight Sparta he was fighting fire with fire. The Athenians were now a bigger threat to his empire than the Spartans would be. Therefore the Great King agreed to support Sparta financially as long as he got complete control of Ionia’s Greeks. With Persia’s financial support the Spartans assembled and manned quickly 80 warships and sailed to the Dardanelles where they stopped the grain ships sailing to Athens. This action brought the Corinthian War to a speedy end. The Athenian dēmos feared being starved into submission as they had in 405. Consequently when Persia summoned to Sardis all those who wished to hear the general peace-treaty which its king wanted, the ambassadors of Sparta and the anti-Spartan alliance arrived with flattering speed.
This paper offers an interesting insight: It wasn't just the value of the Persian gold, but also the simple fact of the existence of Persian coinage kept the wars going. It seems that only Persia had a silver coinage that was useful to be actually used as means of payment, including to be carried about!
Sparta of course did not strike coins until the third century. (Financing the Peloponnesian War: the Peloponnesian perspective, Jennifer Warren, page 317)
Otherwise the city states used a crude form of bullion, which was quite impractical for anything but hoarding wealth:
Hodkinson in his wide-ranging exploration of Spartan wealth as such refers to Spartans stockpiling foreign currencies or sending them for safekeeping to Arkadians (ibid.)
By the end of all this, with everybody lying about exhausted, this backwater named Macedonia comes about and sweeps up the lot.
Including the Persians! ;)
Upvote:1
I'll add a few extra details which may be of use to you since the scope of the question now seems to include events outside the Peloponnesian war of 431–404 BC
Persian gold was said to have made its way into the hands of the prominent Athenian orator and statesmen Demosthenes, who led the opposition forces against Phillip of Macedon and other Pan-Hellenists of his time. It was said that this gold was the main motivator for his staunch opposition to the proponents of a united Hellenic faction.
Aeschines accuses Demosthenes himself of accepting 70 talents from the Persian king after the state of Athens refused 300 in financing a revolt against the Macedonians:
But you, Demosthenes, tire us out with your everlasting talk of Thebes and of that most ill-starred alliance, while you are silent as to the seventy talents of the king's gold which you have seized and embezzled. Aeschines, Against Ctesiphon 239
While Dinarchus says that Demosthenes accepted the whole 300:
Will you not execute this accursed wretch, Athenians, who, in addition to many other crucial blunders, stood by while the Thebans' city was destroyed, though he had accepted three hundred talents from the Persian King for their protection though the Arcadians,1 arriving at the Isthmus, had dismissed with a rebuff the envoys of Antipater and welcomed those from the unhappy Thebans who had reached them with difficulty by sea, bearing a suppliant's staff and heralds' wands, plaited, they said, from olive shoots? Dinarchus, Against Demosthenes 10,18
Plutarch also makes note of Demosthenes accepting the bribes:
Demosthenes, however, was not worthy of confidence when he bore arms, as Demetrius says, nor was he altogether inaccessible to bribes, but though he did not succumb to the gold which came from Philip and Macedonia, that which came down in streams from Susa and Ecbatana reached and overwhelmed him, and therefore while he was most capable of praising the virtues of earlier generations, he was not so good at imitating them. Plutarch, The Life of Demosthenes
You can see by the actions of Demosthenes how much of a hindrance one man under the influence of Persian gold could be. He had convinced the Athenian assembly to send an army with allied Thebans and Boeotians to meet the Macedonians at Chaeronea and be decisively beaten. This resulted in the destruction of the city of Thebes and the end to the conflict which brought most of Greece under Phillip's control.