How did so many people come to live in a desert? Was it not always a desert? What sustained these people to get to 46 million?

The Nile. basically everyone lives within walking distance of the river, and it very clearly brings life.

When I was there it was incredible to see all the (basic) farming and houses and people living in the river valley, and less than 5km away have nothing but blowing sand for hundreds and hundreds of miles.

The Ethiopian dam project should prove to be an interesting test of negotiations and relations between Egypt, Sudan, and Ethiopia.

Massive amounts of food aid combined with patriarchal religion.

There's a political co-factor on food subsidies and keeping prices in a range in the West.

Edit: fertility rate 4.46 births per woman (2021)

The Nile.