The geographic feature that most directly influenced the development of Greek city-states was 2. its mountainous terrain. Greece is a series of island separated by sea and marked with numerous mountains. These mountains kept the region from ever becoming completely unified in ancient times because of the difficulty it took to get from point A to point B. Instead, these mountains resulted in the formation of city-states, smaller political units centered around a single city but sharing a culture similar to other city-states in the area. They were connected by culture rather than politics.