The correct answer is: The mountains and ocean prevented people from uniting into an empire.
Explanation: The geographical features of ancient Greece, particularly its mountainous terrain and extensive coastline, significantly contributed to the development of independent city-states (poleis) rather than a single unified empire. The mountains created natural barriers that hindered communication and transportation between different regions, making it difficult for a central authority to establish control over the diverse city-states. Additionally, the numerous islands and proximity to the sea fostered independence, as each city-state could easily develop its own identity, culture, and governance. The challenging geography encouraged local governance and made the idea of a unified empire less feasible, resulting in the rise of self-governing city-states.