Describe the best way to explain mesopotamia overall in one sentence.

One of the first and most ancient civilizations in which people learned to write, develop large cities, and create a form of government.

The city-states of ancient Mesopotamia were independent cities constructed around temples and entirely self-contained within mighty perimeter walls. City-states were unified with each other only by their shared use of the Sumerian language. They spent most of their time engaged in conflict over resources.