Final answer:
The development of independent city-states in ancient Greece was due to the mountainous terrain which geographically separated communities, leading to localized governance and unique identities (option d). The correct answer is option d.
Step-by-step explanation:
Independent city-states developed in ancient Greece primarily due to geographical factors. The mountainous terrain of the region served as natural barriers, separating groups of people from one another. This separation fostered the development of independent communities, each with its own government, culture, and identity. While some city-states were indeed isolated on islands, it was the mountains more than anything else that hindered overland communication and necessitated the sovereignty of city-states.
Greece's lack of navigable rivers meant that areas could not easily connect and unite under a single government. Moreover, in the Iron Age Greece, the development of independent city-states or polis was also driven by a desire for self-governance among free adult males who participated in the democratic process of their communities. These independent city-states were symbolized by their own acropolis or hill fortress and developed distinct governmental systems ranging from tyranny to democracy.
In conclusion, the primary reason for the development of independent city-states in ancient Greece was geographical division, specifically the mountainous terrain, which created natural separations between communities leading to the need for localized governance (option d).