Uruk, Mesopotamia

In the 5th Millennium B.C. the city of Uruk, 140 miles south of Baghdad was in fact the first city. Uruk's people where the first to live the urban lifestyle. Uruk was the first city think of that. The first time in human history that people come together and cooperated so that larger numbers of us could live side by side. Where one persons skills made it possible for anothr person to build specialized skills in another area. What happened over time so that now we want to kill each other rather than work together and build better cities?