Mesopotamia is Greek for "the Land Between the Rivers" and refers to the areas between the Tigris and Euphrates rivers that developed as part of the Cradle of Civilization, namely Sumeria, Babylonia, and Assyria.
Located in present-day Iraq, this region was home to the first developed civilizations that organized themselves in city-states, developed one of the earliest writing systems in cuneiform and built the first sophicated bits of engineering in ziggurats. Their sophisticated farming and irrigation methods led to the region being called the Fertile Crescent, allowing their civilization to have the resources necessary for the next great innovation; that of the imperial system.
Imperial rule was developed under Sargon of Akkad. While the idea of singular rule may seem trivial in regard to civilization, it is important to remember that the administrative knowledge necessary to develop and maintain such a widespread ruling organization is indeed a mark of a developed civilization. Babylon took these ideas further that culminated in the brutality of Assyria, demonstrating an important lesson of how rulers of excess, be it in violence or indulgence, never last that long. The style of administrative empire shown by the civilizations of Mesopotamia became an important lesson for Ancient Egypt and subseqent civilizations.