Why did civilizations first arise along the Fertile Crescent?

The fertile soil led to crop production. That allowed a population to grow in the area which was the beginning of a civilization. The larger population with a stable source of food attracted others, some of whom only wanted to take food without work or payment. The populace had to band together for protection, establish a policing force, which required food/payment/taxes, with a leader. This eventually grew into a full fledged civilization.