What part of the reason region fall between the Fertile Crescent

The Fertile Crescent is the region in the Middle East which curves, like a quarter-moon shape, from the Persian Gulf, through modern-day southern Iraq, Syria, Lebanon, Jordan, Israel and northern Egypt. The term was first coined in 1916 by the Egyptologist James Henry Breasted in his work Ancient Times: A History of the Early World, where he wrote, "This fertile crescent is approximately a semi-circle, with the open side toward the south, having the west end at the south-east corner of the Mediterranean, the centre directly north of Arabia, and the east end at the north end of the Persian Gulf."