When people are asked today what they think the land in Iraq is like, most would say desert. And in a sense it is. It doesn't rain much so in that way it is a desert, but the land between the Tigris and Euphrates rivers is very fertile. Food crops grow readily if they have water.
When people first moved into the region between the Tigris and Euphrates, they found living pretty easy. There was wildlife to catch, fish in the rivers, and edible vegetation growing wild. So they stayed.
Soon they found that they could grow their own food if they tended the land. Then they figured out how to get river water into the fields, and crops grew in abundance. Other tribes saw the wealth and food the people of the river valleys had, and started raiding to take it. So to protect themselves, they started building walls around their town. Cities grew from these towns.
As they learned how to grow them, the people of the Mesopotamia area planted and grew wheat, barley, dates, cucumbers, onions, apples and many different herbs and spices. They also raised sheep goats and cattle. Thus a civilization grew along the two rivers.