I'm not an expert on the matter. I just read about the fertile crescent & how at its peak it wasn't a desert like it is today and that temperatures and sea-level were both lower than today. For example the persian gulf (today underwater) "was an extensive region of river valley and wetlands" https://en.wikipedia.org/wiki/Persian_Gulf#History when the ancient civilisation of Sumar developed there.

I have no knowledge about the eastern portion of Egypt (Sinai?) being richer than the western one, afaik the wealth of Egypt was always centered around the nile and nile delta (even today). That's probably what the breadbasket refers to.