Why did Mesopotamia city-states flourished? Was it due to specialized labor or conquered an area large enough to make themselves self-sufficient.

Answer 1

Read these VERY carefully:

http://www.ancient.eu/Mesopotamia/

http://www.worldology.com/Iraq/mesopotamia_advanced.htm

http://www.penfield.edu/webpages/jgiotto/onlinetextbook.cfm?subpage=1525827

http://www.mrdowling.com/603mesopotamia.html

Answer 2

PS -- It happened over a long period of time, and it had far more to do with developing human abilities and talents than conquering other people!