How did the natural wonders of Africa inhibit the spread of the Egyptian civilization?

The Sahara Desert limited how much land the Egyptians could settle.
Unpredictable flooding made much of the Nile River Valley too dangerous to develop.
Mount Kilimanjaro on the southern end of the Nile River confined trade to people within Egypt.
The Ngorongoro Crate prevented the Egyptians from trading with people who lived upriver.