How did the physical geography of Greece cause Greek-speaking peoples to develop separate isolated communities?

The geography of Greece caused it to separate into city states. This is because of the mountainous terrain that isolated several parts of Greece. These mountains were very hard to get around and caused every isolated city state of Greece to develop it's own culture. For example Athens developed a strong naval unit because it was close to the sea. AThens was also the most knowledgable about other cultures because the sea made for easy trading.