Not books, but a few years ago the BBC broadcast a series of programmes called Lost Kingdoms of Africa. There were eight programmes in total. The very first programme was on Nubia.

Unfortunately, the programmes are not available on iPlayer (the BBC's online TV and radio catch-up service, which isn't available to anyone outside the UK). But do a search on YouTube and you'll find all eight episodes.

Here is a link to the BBC site that lists each episode

http://www.bbc.co.uk/programmes/b01bgnb1/episodes/guide

For East Africa you can't beat anything by Richard Reid. He also has a wonderful book on Africa from 1800 to the present you may enjoy: https://smile.amazon.com/dp/1405132655/ref=wl_it_dp_o_pC_nS_...

I tend to only focus on E Africa when reading (since I live in Uganda), but Richard Reid's writings are the best for understanding the region's history.

There are many books by scholars but it is probably not what you are asking for. But you can read a lot as usual on the English Wikipedia [0]. I wrote recently a small book in French about this subject and had entertained the idea to write an augmented version in English in one or two years.

[0] https://en.wikipedia.org/wiki/History_of_Africa