Follow up question:

What areas historically relied on the Nile harvest for food? That is to say, what populations outside of Egypt relied on food imports for their very existence. I've heard about the Hedjaz region (Mecca, Medina, surrounding area), and Rome during its heyday both relied on Egyptian food imports. Are there any other areas that relied on Egyptian food to such an extent?

Feel free to elaborate on or answer only one question (while still following the rules). This is no doubt a very complex question, and probably worthy of its own thread.