What promoted civilization in Mesopotamia?

Many different factors led to the early development of a sophisticated civilization in Mesopotamia, and the confluence of these factors created a virtuous cycle in which cultural, economic, and demographic advantages became mutually reinforcing.
Perhaps the most important building block of the development of Mesopotamian civilization was agriculture. The fertility of the soil, availability of water for irrigation, and prevalence of readily domesticable species meant that Mesopotamia was one of the earliest civilizations to develop agriculture. This created a foundation for urbanization and also a food surplus that allowed for increasing specialization of labor and technological advances. This specialization of labor led to major technological innovations to the plow, the wheel, writing, chariots, and sailboats, all of which in turn led to greater trade, agricultural productivity, and ability to develop institutions capable of coordinating large numbers of people over substantial territories.