Why was ancient Greece hundreds of tiny countries instead of one?

Ancient Greece was hundreds of tiny countries because mountains cut the land into pockets, and each pocket ran its own affairs and guarded its independence. About 1,500 Greek city-states are known, each called a polis (plural poleis). When the Mycenaean civilization collapsed, no powerful state replaced it, and settlements separated from their neighbours by mountainous terrain grew into small independent communities.

A polis was more than a town. It was a homeland, with its own constitution, its own citizens and a demand for their loyalty. Only free, land-owning, native-born men counted as full citizens, and those men did the fighting, since city-states could not keep professional armies. Being Athenian or Corinthian was something you were, in the way a modern person is French or Japanese.

The strange part is that the Greeks knew they were one people. They shared a religion, a basic culture and a language. Yet the independence of each polis was fiercely defended, and unification was something rarely contemplated. When some city-states allied against the second Persian invasion, most poleis stayed neutral, and once the danger passed the allies quickly returned to infighting.

Greek colonies show the same pattern. Settlers carried the polis idea around the Mediterranean, and Syracuse, Naples, Marseille and Istanbul all began as Greek colonies. Each was an independent city-state, not an outpost taking orders from a mother-city. The rest of this path is the story of what those hundreds of small worlds did, and what happened when a few of them tried to rule the others.