Final answer:
The isolation of Greek city-states was caused by rugged mountains, which led to independent political development and reliance on the sea for trade.
Step-by-step explanation:
The isolation of Greek city-states was primarily caused by the geographic feature of rugged mountains. Unlike civilizations such as Egypt or Mesopotamia, which benefited from great rivers to support agriculture and encourage trade, Greece was characterized by mountainous terrain, making travel and communication difficult. This contributed to the development of independent city-states, each with its own system of government and culture. The mountain ranges and challenging landscapes not only fostered a sense of autonomy and regionalism but also necessitated a reliance on the sea for trade and interaction with the wider world. The difficult topographical conditions of Greece, with its poor, rocky soil and scarce mineral deposits, thus played a crucial role in shaping the ancient Greek civilization.