Hey there!
The geography of Ancient Greece was very different compared to that of other civilizations and areas.
There were many mountains and lots of rocky soil, as well as very few coastal plains to settle on. That lead to isolation. Greek city-states were isolated because of the harsh and mountainous geography. It was hard to travel between them, and therefore many city-states were created, each developing their own cultures.
That's exactly why uniting Greece was necessary- making sure everybody spoke Greek and had similar customs to create a strong and unified empire. This was what Alexander the Great did with Hellenistic culture, and it got him quite far.
Hope this helped!
