What were some of the major factors in the Greek victory over the Persian Empire?

The Greek city-stated did not have a 'victory' - they wore down over 50 years the Persian resolve to establish peace in the eastern Mediterranean by incorporating all the mainland Greek city-states into their empire in order to control their hostile activities. After 50 years, the Persians gave up and left the Greek cities to go back to their habitual fighting amongst themselves.

The factors of this Greek success against Persia were:

Setting aside their habitual fighting between each other and uniting at crucial periods of the 50-year struggle against Persia.

Superiority in naval strategy and tactics.

Coordination of land and sea power at crucial periods.

Being the underdog drove them to desperate defence.