How did Greece delay the Persian invasion?

Answer 1

After failing in their punitive mission against Athens for its support of Greek city revolutions in Asia Minor within the Persian Empire, Persia decided to incorporate the Mainland Greek cities within its empire and appoint a Persian governor to keep them quiet.

This invasion was delayed because of a revolt by Egypt which was part of the Persian Empire. Then King Darius died and the invasion was again delayed until successor king Xerxes got control. He then sent emissaries to bribe the Greek cities to submit, which many did, and he was then faced with the cities of southern Greece holding out. So after ten years of delays, the Persian invasion got going.

Xerxes mounted a two-prong invasion - a land force and a naval force. The naval force protected his essential sea supply line and threatened the Greek cities, which therefore kept their land forces at home, allowing the Persian land forces to pick the cities off one at a time.

The Greeks decided they must first destroy the Persian navy to remove this naval threat and allow their cities to send out their armies to concentrate against the Persian army and make a real fight of it. They blocked the pass at Thermopylae with a small army force to compel the Persians to turn the position with a naval attack; the Greek fleet was lying in waiting to pounce on the Persian navy. Unfortunately the Greeks lost the naval battle and retreated to try again (this time successfully) at Salamis in the south. The holding (not delaying) force at Thermopylae, its mission now finished, was withdrawn under cover of a stay-behind contingent from Sparta and Thespia.