How did your graphic factors encourage independence among ancient Greek city states?

Unlike many other ancient nations which were next to the one another and traveling by land across them was feasible, Greek small states or "polys" were separated from each other by mountains and the few existing roads were not easy to traverse. Also, the poor soil of inland Greece prompted ancient Greeks to build their cities close to the sea, so that they could have a way of communicating and trading more easily. This resulted in a fragmentation of Greece which was divided into over a dozen of city-states, independent from each other albeit staying in close touch with each other either as allies or enemies.