They set about destroying the Persian fleet which threatenedeach of the Greek city-states with amphibious invasion and so thecities kept their armies at home to defend themselves until the seathreat ceased.
When the Persian fleet was destroyed at Salamis, the citieswere able to send their armies out to join up at Plataia thefollowing year.
The loss of the Persian fleet also left its sea supplyvulnerable and in fact they had to send half their army home asthey could not feed them in the upcoming winter.
Superior tactics –
At Salamis they split the Persian fleet and defeated it indetail, also neutralising the larger Persian ships in narrowwaters.
At Plataia they kept to broken ground and so avoided thesuperio Persian cavalry, and were able to defeat the inferiorPersian infantry.