to threaten the Greek cities with amphibious attack so thatthey kept their armies at home to defend themselves, and so couldnot concentrate against the Persian army which could then pick thecities off one by one.
to protect their supply line from the Greek ships, which inthose days of slow, low capacity wagons, had to be by seatransports.
The Greeks centred their attention on the Persian navy to try todestroy it and with it the Persian plan. They blocked the pass atThermopylai, which forced the Persians into a sea battle tooutflank the block. This failed, so they tried again at Salamiswhich was successful, and the remnant of the Persian fleet waswithdrawn to Mykale in Asia Minor, leaving the Persian army withoutadequate supplies in such a poor country as Greece.
Now unable to supply his army during the winter, Xerxes took halfhome and withdrew the rest to the north where they could getsupplies. Next spring the southern Greek cities, the threat totheir homes gone, were able to concentrate their force at Plataiaand defeat the reduced Persian army and its Greek allies. They wenton to destroy the remnant of its fleet at Mykale.
Sea power was the key to the campaign. The Greeks, with inferiorships and ship numbers set battles in narrow waters where theyneutralised the superior number and size of the Persian ships, andwon the key Salamis battle. They were boosted by the fact that theywere fighting for hearth and home, while the Persian fleet was madeup of contingents from subject cities of Phonecia, Asian-Greeks andEgypt, who really didn’t have the same motivation.
Popular stories of the war usually omit the central theme – thatboth sides had well defined and clever plans of action. Both hadtheir successes. The Greek victory at Salamis turned the resultdecisively in their favour.