What dictated the division of ancient Greece into many small, independent city states?

A. the 7 of the region

B. the population of the region

C. their establishment by the region's leaders

D. the culture of the region

The one answer that I am missing among the options, but which is the correct one is: the geography of the region (I assume that that's what was instead of the "7" in the first option).

It was very mountainous, with valleys and islands on which people lived - meaning there was a natural separation between the different settlements.