That needs to be in the sequel to the sequel:
“300: Rise of City Hall - Boss Tweed-mistocles”!
Heh... the comic book on which that silly "300" movie was based seems to have had much more reach than grasp. There's a bogus recent version of the famous epigram marking the mass grave -- the fake ending is the addition of "the Athenians never came."
The Spartans were on the take from Persia, that's obvious, no evidence of course -- they claimed they couldn't participate in the defense of Greece from the Persians' big invasion by sea, and the fastest runner in Greece returned with the bad news. The Athenians led the Battle of Marathon, bearing most of the burden, and the participating Greeks whipped the Persians. They left a guard at the site, then hurried back to the city to prevent a second Persian landing. That spoiled the Persian plans, and gave Greece (particularly in Athens) ten years to prepare for the next Persian invasion.
A few days after Marathon, the Spartan army arrived, obviously to take over control of their vanquished Athenian enemies -- and imagine their surprise.
The rise of the demos in Athens stemmed from an earlier Spartan invasion which had installed a Spartan puppet as a despot to rule Athens. In a later generation, after Athens' defeat by Sparta in the Peloponnesian War, installation of another Spartan puppet despot followed. That domination ended because the Spartans turned their attention to the Thebans. The Theban victory at Leuctra marked the end of generations of Spartan domination of Greece and the freeing of all their slaves.