ok and now a serious answer:
there were very different tribes, in the same way that “Native Americans” are not all one nation. Most of them fought with each other all the time and eventually formed city-states.
The original Greek “phyla” (meaning something like “tribe” “clan” or “large family”) were the Pelasgoi, but by the classical times most of the Greeks were decendants of Dorians (Sparta etc in the south) Achaians (Athens, Corinth and central Greece) Ionians (on the coast of what today is Turkey) Macedonians (in the north) and Aeolians (in the northern Aegean islands). The Minoans and Mycenaeans were older tribes, Minoans living in Crete and Mycenaeans in Peloponese.
There were also the Thracians, which Greeks themselves considered to be “foreigners”, even though they spoke the same language and had similar gods. I think one could compare it to the way modern Americans see Canadians. After Philip II conquered all the other tribes and his son Alexander expanded his empire to include half the world, the idea of “hellenism” was born, with all Greeks realising they had a lot more in common (as opposed to Persians or Indians for example) than they had previously thought. It doesn’t mean they became a country in the modern, nation-state sense we have today, but they saw themselves as having more similarities than differences.
Some theorists have suggested that Egyptians are closely related to the earlier Greek tribes, and with other Mediterranean tribes such as the Phoenecians they are called “protohellenes”. This is a very controversial theory though, it’s very hard to determine when a national identity is born, especially when you’re talking about people who lived thousands of years ago and never saw the world the way we do.
As for the modern-day populations of those countries: modern Egyptians have decended from Arabs and probably have very little to do with the original Egyptian populations. Similarly, Greeks have been conquered and interbred with several other nations over the last 3000 years, so even though there’s probably some Achaian blood in many modern Athenians, most Greeks have probably decended from a variety of different nations. Which is why modern-day Spartans look a lot darker than the blonde Dorians who built the city all those centuries ago.
I just realised it’s basically what Val just said, but in much smaller letters lol