Athens Democracy - 510 B.C.
Having their landing at Phalerum turn into a farse, in the following year, 510 B.C., the Spartans dispatched a larger force, and organised a full scale invasion, this time led by King Kleomenes I to invade Athens. Once they came to Attica they met up with the Thessalian horsemen. This time the Spartans put them to flight and after a short battle the horsemen retreated and headed straight back to Thessaly. Kleomenes I and the Spartans proceeded to Athens, where they found the tyrants boarded up in the acropolis. While they had planned well to be holed up in there, they didn't plan that the children of the tyrant were caught trying to flee the country. After five days they quit the acropolis and were allowed to leave for their estate in Sigeum, on the Dardanelles, where Hippias soon set up a government-in-exile.
After a brief power struggle to gain control of Athens, Kleomenes I directly tried to dissolve the council and put in charge 300 of his followers. The council didn't stand for this and Athens started to revolt. Kleomenes I withdrew with the Spartans back to Sparta.
In this way Sparta unwittingly allowed Athens to evolve into a democracy.
Athens in a state of tumoil recalled Cleisthenes (the persuader of the Pythoness) from Delphi and gave him power. They sent envoys to Sardis to make an alliance with the Persians, for they knew that war would follow with the Spartans. King Darius requested earth and water for an alliance with Athens, to which the envoys agreed; but were put into disgrace by the Athenian people on their return, they would not capitulate to this.
'The Greco-Persian Wars' by Peter Green published by University of California Press 1998