Final answer:
The transition from nomadic hunter-gatherer groups to settled agricultural communities led to the rise of complex societies. Mesopotamia is an example of an early state culture that developed as a result of this transition.
Step-by-step explanation:
One explanation for the rise of complex societies is the transition from nomadic hunter-gatherer groups to settled agricultural communities. This transition allowed for the development of sedentary cultures, which established governments, writing and number systems, and hierarchical social systems. An example of an early state culture that fits this theory is Mesopotamia. The city of Uruk was one of the first true cities and it developed a complex Mesopotamian culture with its own writing system and religious beliefs.