Answer:
The geographic feature that exposed the Maurya and Gupta Empires to invasion was the Hindu Kush passes.
Step-by-step explanation:
The Hindu Kush passes are elevated mountain chains that goes through around 800 kilometers. It exposed the Mauryan and the Gupta empires which were the most successful empires of Ancient India. Historically, the access through Hindu Kush always was of great military importance. Alexander the Great for example, crossed the mountains with his army in 329 BC, during a campaign to suppress a riot in a province of the Persian Empire.