Why did small independent communities develop in ancient Greece?

The Greek city states (polis) were formed out of the Homeric period because of the iron age and Greece's impossible terrain. During the Homeric period the Mycenaean Greeks were in control of most of Greece's vast areas since their kings had bronze weapons. When iron was discovered that enabled anyone to make weapons, the kings lost their empires and the people began to form communities according to Greece's natural borders.