What was the main goal of the Persians in all their attacks on Greece?

Answer 1

The Persian Empire contained hundreds of Greek city-states, many of which had revolted aginst Persian rule, encouraged by the mainland Greek city-states. Persia realise that this would continue unless the external Greek city-states were brought under control, so it decided to bring them all under control of Persian provincial governors and appoint local tyrants to keep them quiet.

Answer 2

the plan was to get as much men as the could get and just come together and go against the greeks.

Answer 3

to establish the peace in their empire being broken by Greek revolutions and attacks.