Final answer:
The mountainous terrain of Greece fostered the development of independent city-states by providing natural isolation and protection, thereby encouraging local autonomy and cultural development within each polis.
Step-by-step explanation:
The geographical feature that encouraged the development of independent city-states in ancient Greece was the region's mountainous terrain. This difficult topography resulted in isolated valleys and islands, each developing into a self-governing polis, or city-state. The natural fortifications provided by mountains and the sea fostered a sense of independence and made it challenging for a single power to control the entire region.
Greek society was highly insular, with fierce loyalties concentrated around one's polis. These regional divisions, coupled with the establishment of colonies, propagated a shared Greek identity throughout the Mediterranean. The culture and political structures of the city-states—varying from democracy to oligarchy—were shaped by this geographical fragmentation, which allowed local customs and governance forms to flourish without overarching imperial control.