Main idea of this paragraph?

In southern Mesopotamia, (the area known as Sumer), the number of settlements grew from 123 between 4000 and 3000 BCE. The average size of settlements grew, and the first cities arose. During the third millennium, an estimated 80% of the population was urban. In Egypt, there were similar increases in numbers and sized of settlements at about this time. Egypt, however, remained more village based than either Mesopotamia or the Indus valley. In the Nile valley, fewer cities developed and the population spread more evenly.

Question

Main idea of this paragraph? 

In southern Mesopotamia, (the area known as Sumer), the number of settlements grew from 123 between 4000 and 3000 BCE. The average size of settlements grew, and the first cities arose. During the third millennium, an estimated 80% of the population was urban. In Egypt, there were similar increases in numbers and sized of settlements at about this time. Egypt, however, remained more village based than either Mesopotamia or the Indus valley. In the Nile valley, fewer cities developed and the population spread more evenly.