Mesopotamia literally means between rivers, and the rivers it refers to are the Tigris and the Euphrates. In early agricultural societies, being near rivers was important because it provided fertile soil.
One example city in Mesopotamia was the Sumerian city of Uruk, which is the hometown of King Gilgamesh in one of the oldest stories ever written, The Epic Of Gilgamesh. This brings us to one of the most important things that came out of Mesopotamia – writing.
They developed a writing system which is now known as cuneiform. A lot of it was used to record transactions, but eventually it was used to tell stories like Gilgamesh. Their writing system was so flexible that over the span of 3000 years it was adapted into over a dozen major languages.
As cool as writing is, I think the other things they invented are just as interesting.
They came up with a base 60 counting system, which is the origin of 60 second minutes, 60 minute hours, and 360 degree circles.
They studied the sky and divided the year into 12 periods named after constellations. They divided the week into 7 days named after 7 gods, which represented the observable planets in the sky.
They came up with a law code which was the basis of a standardized justice system. This is the origin of an eye for an eye. It also introduced the presumption of innocence.
They also invented this amazing thing called the wheel.
This long list is probably missing more than half of their inventions. A lot of great things came out of this region, though to clarify, these are different kingdoms ruling over the same region, not one kingdom.
Still, it is mindblowing what these people accomplished and contributed to human knowledge.