Why was Macedonia able to conquer Greece?

Philip never conquered Greece. He united Greece under Macedonian Hegemony in order to attack Persia and free the Greek states in Asia Minor that the Persians were harassing. He did this by developing a professional army, through subversive means and also by force. The historian J. B. Bury explains:

  • As the hegemony or first place among Greek states had passed successively from Athens to Sparta, and to Thebes, so now it passed to Macedon. The statement that Greek liberty perished on the plain of Chaeronea is as true or as false as that it perished on the field of Leuctra or the strand of the Goat's River. Whenever a Greek state became supreme, that supremacy entailed the depression of some states and the dependency or subjection of others. Athens was reduced to a secondary place by Macedon, and Thebes fared still worse; but we must not forget what Sparta, in the day of her triumph, did to Athens, or the more evil things which Thebes proposed.