The people of Ancient Greece lived in small, isolated communities that eventually grew into large city-states. Why were these communities isolated from one another?

Greece has many mountain ranges, and travel by land can be difficult. Only about one-fifth of the land is suitable for habitation and farming, and much of that exists as pockets of fertile land that are isolated from each other. The first ancient communities were attracted to these areas but thus grew independently from each other.

Also, much of Greece is peninsular. Large irregular areas of land, including many islands, are surrounded and separated by the Mediterranean and Aegean Seas.