Ancient Greek philosophy didn't evolve in a vacuum. If anyone really happens to be interested in the subject a good source might be 'The Shape of Ancient Though

Ancient Greek philosophy didn't evolve in a vacuum. If anyone really happens to be interested in the subject a good source might be 'The Shape of Ancient Thought' by Thomas McEvilley which traces the co-evolution of ancient Greek and ancient Indian philosophy starting from the time both Greece and India were subordinate to the Persian Empire and interacted extensively in places like Persepolis. This interaction continued even after the subordination of Persia to Greece and later to Rome.