Even when fighting against Persians or being conquered under Alexander the Great where never truly unified, just common cultural traits.
The myth of a single unified Ancient Greek culture is a modern fabrication made during the rise of the nations in an effort of fabricate a common past for all folks living under modern states and give a legacy and an identity other than one of the provinces of Rome descendant of the ancient tribes who populated the peninsula. And my understanding is that the same happen with other European pre-romantic cultures like celts, Gauls, Britons, Germans and lots of other lost and forgotten mythological elements from Europe which were praised and recreated to differentiate modern states from their neighbors.
dialects with regional substrate and vulgar varieties; koine written greek is a rather late standard, perhaps not byzantine, but koine literally means "written", in contrast to spoken.
> lifestyle
like what? Sedentary, sure.
> music
music-ians, who were not the same everywhere
> alphabet
again, regional variants exist, writing style wasn't fixed
> commerce
commerce is competition, so how could it be unified? associated towards outsiders, perhaps.
> military style
I wouldn't know about that, but Sparta vs Athens thousand years earlier would be a common counterexample
It's debatable how hellenized the Greeks on the anatolian cost were, the Lydiand, moesians and cetera. "barbaros" relates to speech first and foremost, though I am not buying the etymology. Speakers of other mother languages would have reasonable trouble getting the pronounciation right, so a Scythian, Tracian, Dalmation or otherwise "Celtic" Slave would appear hard to comprehend.
If you are generalizing a millenium of history, you are all history barbarians.
Could we agree that Athens and Syracuse were more similar than Athens and Persepolis?
How about common myths and goods? Olympic games that paused wars? Delphi were in "center" of helenic world? And ancient debate if Macedonians are "true Greeks" or "barbarians"?