[Yef]

The world today resembles classical Greece's city-states, on a diferent scale.
They never managed to create a single Greek state. They had quite a few leagues, some very succesful, but unification was only achieved when the Macedonian Falanxes decided to march south. Short lived unification, by the way.


Then a there is the other matter.
Unification tend to slow down progress due to the lack of competivity. The hellenistic kingdoms, the succesors to Alex's Empire, achieved more during the 2 centuries of rivalry between them than after the Roman unified them by conquest.

As another example, the success of Western Europe, that from the "dark ages" went all the way to an almost 5 centuries long global domination, was fueled because no single power managed to unify Europe after the fall of Rome, while in every other area in the world empires raised one after another, with just relatively brief periods of political fragmentation (ie: China, Middle East, etc.)