You can find the answer to this question by looking in Chapter 8. There (beginning on p. 138 in the paperback edition of the book), Diamond lists a number of advantages that were enjoyed by the Fertile Crescent. These advantages include:
- A high percentage of wild plants that could be domesticated.
- The largest area with the Mediterranean climate that is good for farming.
- The most variation in climate over the years as well as within each year. This allowed for the evolution of many annual plants.
- Lots of different altitudes and topographical features within a small area. This makes for a diverse array of plants that are harvested at staggered times of year.
- Lots of big animals that could be domesticated.
- It wasn't as good for hunter-gatherers so they did not really compete with the people who were starting to live a sedentary, farming lifestyle.