they had large fields of wild grain growing there. They first formed villages because they had a large natural food supply, then learned to plant it themselves. Once they had learned to expand the food supply, they could have people learn specific trades and specialties as villages grew into towns, etc. This allowed technological advances as well.
They also had the advantage of domesticable animals such as donkeys, horses, cattle, sheep in the area to use as food and draft animals... they had all the natural advantages there, with out having to import any thing.
