How does the geography discourage geek unity?

Greece was mountainous on the mainland and also was composed of numerous islands. As a result communities were isolated and could be compared to Mesopotamian city-states.

Greece is full of mountains and seas. The difficult terrain prevented efficient communication between people of different locations, making people feel as if they were isolated from the other parts of Greece, and creating a sense of independence. City-states formed as a result of this isolation. Also, where people lived determined their way of life, which lead to the formation of different cultures, which had the potential to create conflict. City-states often warred with each other.