There are a multitude of answers to your questions. Certainly, we know a lot more than you might think given their marginalization in the grand narratives of history we received. But I have a couple of questions before I can answer further. The most important is what you mean by "ancient". Asante (or, if you prefer, Ashanti), for example, is really a 17th-19th century state. Do you want to know more about the vast and complex network of states in the region in this era, or do you want to dip back much further in time? Also, by West Africa do you mean to include the Lake Chad basin and Bend of the Niger River (Inland Niger River Delta)? Or do you prefer to focus on the coastal areas you are suggesting above?

One place to start is with the UNESCO General History of Africa volumes. I know I know, they're a little bit outdated now. Revisions are coming, or so we're assured. However, they were also groundbreaking, written for a general (if educated) audience, were written by leading scholars (most of them Africa-based), and break things down by region and date. Also, they can be read online for free. For example, I would direct you to [this link] (http://www.unesco.org/new/en/culture/themes/dialogue/general-history-of-africa/volumes/complete-edition/volume-iv-africa-from-the-twelfth-to-the-sixteenth-century/) for Volume IV, which covers the 12th-16th centuries. Just click the "Read the complete volume online" button .

But I'm happy to also answer your question as best I can if you can give me a bit more detail about the scope of your interests.

There is an article published in Archaeology magazine (volume 64 number 4, July/August 2011) titled The Nok of Nigeria. There is an excellent quote in it by an anthropologist George Murdock who states that for every ton of earth moved on the Nile, only a teaspoon is moved on the Niger. The article attributes the lack of knowledge on the Nok of Nigeria to corruption in the Nigerian government, expensive visas and a chaotic political situation. There is also the extensive looting of these sites which has removed many artifacts as well. Murdock made his quip in 1959 and perhaps things have improved, but an article in the African Studies Review titled Contradictions in Creating a Jihadi Capital: Sokoto in the Nineteenth Century and its Legacy indicates things have not. The author Murray Last notes that many historical buildings in the former northern Nigerian state of Sokoto have been demolished and refurbished with modern materials such as concrete instead of the traditional mud brick and rebuilt in foreign styles (Saudi Arabian), historical city walls have been knocked down to allow improved vehicle traffic and history programs in Nigerian Universities are struggling due to a lack of interest (Last believes this decline due to the elimination of history in the Nigerian primary school curriculum).

The lack of knowledge about Africa could be attributed to unstable political situations preventing archaeologists from accessing sites, old sites being demolished due to utilitarian purposes, lack of domestic interest in history and extensive looting. Still there has been some excellent work done about Africa and one source I found useful was Graham Connah's African Civilizations: An Archaeological Perspective.