Your directions are east and slightly south from New York.
The correct answer is - rugged mountains and hills made inland contact difficult.
While this answer may be surprising it is nevertheless true. At the time, there were no modern ways of transport. Moving from one location to another greatly depended on how passable a terrain was. Since the terrain between Greek city-states was very difficult to pass, maintaining autonomy and the sense of belonging only to the city was strong instead of belonging to the country.
