They lived on the island of Crete.
This was important because they started to trade ideas and learned about each other's cultures. The Mycenaeans began to copy some of the Minoans ideas and were ultimately were able to replace the Minoans as the major civilization on the Mediterranean.
The population started to come down because the Greeks had fighting among the kingdoms and they weren't getting anything done. Then trading stopped and farmers could only grow enough to fill their own families bellies. People stopped writing and inventing. This is why historians call this time the Dark Age.
Since so many people left the Mycenaean civilization, Greeks started to make colonies and expanding their culture. The population increased.
Famers and merchants and other craftsman demanded change from the nobles. They overthrow the nobles.
They say he was great because he is the one who pretty much created the Persian empire. The empire was largest one the world had yet seen.
The Greeks comes together to form the largest army ever. The Persian empire falls.
Tyrants who had been popular when they were overthrowing the nobles were not longer popular because the same problems were no longer there. As a result most city states became either oligarchies or democracies.
A bunch of city-states came together just in case the Persian empire comes together again so they'd be strong enough.