Ancient Greece
The geography of Greece, which is divided and sub-divided by hills, mountains and rivers, certainly contributed to the nature of ancient Greece. On the one hand, the ancient Greeks had no doubt that they were "one people" since they had the same religion, same basic culture, and same language. However, each city-state, or polis, was independent; unification was something rarely discussed by the ancient Greeks. Even during the second Persian invasion of Greece, although a group of city-states allied themselves to defend Greece, most poleis remained neutral, and after the Persian defeat, the allies quickly returned to infighting.