Without the amount of rainfall that happens in that region, the area would not be suitable for growing crops like grain to sustain a people that would want to live there. With rich soil that is plentifully watered by the rain, people could settle permanently in the region because they could grow their own food.
Twelve inches of rainfall and/or irrigation was needed to raise a crop of grain and the Fertile Crescent was the only place where there was enough water to grow crops
The Fertile Crescent is located in an area and latitude that has enough rain to support growing grain.
Previously, many of the ancient people were hunters and gatherers. They would travel following herds in order to provide for their families. They gathered food along the way. Because of this lifestyle, they were continuously on the move and traveling in small groups.
In the Fertile Crescent area, these people realized they could grow their own barley. Since this crop only needed 12 in of rain annually, they knew that the plants would get enough water. This discovery changed everything. No longer, did the people need to stay on the move. They could settle down and have their crops and their homes and they no longer had to stay in small groups. Because of this, cities developed and eventually empires.
The rainfall requirement for land to produce barley and wheat is about 12 inches per year. The Fertile Crescent is in this span of latitude that provide this condition. With the grain production capability and storage ability, the domestication of animals is feasible. People will settle there . Innovations and technologies will increase because of the people activities. Society, countries and eventually empires form.
The idea of fertility is quite different from our perception and understanding of it. For example, not every place in the Middle East can grow grain as it requires sufficient rainfall. However, the rainfall in the Fertile Crescent is enough to grow grain. Therefore, we can consider it fertile land among the regions that are mainly dry and do not have water for agricultural purposes.