Over time, more and more people settled, and the new tools and technology available made social life more complicated. Economic changes allowed people to gain skills other than farming.
Social changes include defined rich-poor social class, organized religions and rituals involving nature gods, and lots of labor for advanced technology.
The city of Sumer was the first to be defined as a city as we know it today. It was a center of trade, workers specialized in different skills, institutions like churches and government buildings, record keeping methods, and advanced technology.