History of the Peloponnesian War

But when the navy of Minos had been established, navigation between various peoples became saferfor the evil-doers on the islands were expelled by him, and then he proceeded to colonize most of them—and the dwellers on the sea-coast now began to acquire property more than before and to become more settled in their homes, and some, seeing that they were growing richer than before, began also to put walls around their cities.

Their more settled life was due to their desire for gain; actuated by this, the weaker citizens were willing to submit to dependence on the stronger, and the more powerful men, with their enlarged resources, were able to make the lesser cities their subjects.