Mesopotamia was located between the Tigris and Euphrates Rivers in modern-day Iraq. It was the site of the earliest civilizations, with many city-states forming along the fertile river valleys where agriculture flourished. The Sumerians, who lived in the region between the rivers, developed writing, schools, and advanced cultural and technological innovations like irrigation and city planning, making Mesopotamia the cradle of civilization. However, constant warfare between the independent city-states left Sumer vulnerable to conquest by other groups like the Babylonians.