Final answer:
The Mesopotamian civilization was characterized by independent city-states with stratified social hierarchies, where rulers and religious leaders were at the top and common laborers were at the bottom.
Step-by-step explanation:
A key feature of the social organization of the Mesopotamian civilization was the existence of independent city-states. Each city-state in Mesopotamia was like its own small country, with its own ruler, laws, and gods. Cities were often at war with each other or with external enemies but could also form loose confederations or leagues under a more centralized rule, especially during periods of trade expansion. The social structure within these city-states was highly stratified, with a clear hierarchy from rulers and religious leaders at the top to the common laborers and farmers at the bottom. The possibility of social mobility did exist, as families could potentially accrue wealth through trade and move up in social standing.