questions about sub-saharan African kingdoms?

Question

O.k. I have learned about various kingdoms that developed in Africa. My question is why did they leave so little behind? For example the Sahelian Kingdoms of Mali, Songhai, and Ghana, we know from history that they were great, however, unlike the Egyptians ,they didn't leave much behind. Yes, Iknow there is a beautiful mud mosque in Mali, but Why didn't they built greater monuments like pyramids and temples, stuff like that. Could stone not be found in the Sahel? Were there no other resources they could use ?
2nd question Concerning the great Zimbabwe, it is good that the ancient zimbabweans, who are supposedly the ancestors of the modern day shona people ( who are the majority in zimbabwe) built the city However, why didn't they built all of their cities like that of zimbabwe, instead of only two { the great zimbabwe and Khami, another city though smaller than zimbabwe.}?

Answer 1

It is possible that whatever they did leave behind was appropriated by successors. Egyptian monuments lost a lot of their original glory to grave robbers and construction material seekers of later generations, so this could (and did) happen in other places as well...

As to your second question, the answer is rather obvious. Many ancient empires were built by force, with the metropolis and its army living off the conquered lands. So the imperial government only wanted to have one unrivaled city, the one it resided in.

Answer 2

There are a variety of reasons why we don't tend to have as many remains or know as much about sub-Saharan African civilizations.
One is, as you hint at, that stone is not easily obtainable or easily workable in all areas. Or, if it is, if there are other building materials that are easier to use, more flexible to work with, and more abundant, there may be a choice to avoid working in stone or to limit the amount of work in stone. Stone lasts far better than other building materials, such as mudbrick or wood, especially in environments that are relatively moist. So, there may well have been and probably was a great deal more monumental architecture in ancient sub-Saharan Africa than we are now aware.
In addition, preservation in sub-Saharan Africa tends to be worse that it is/was in Egypt. Egypt is predominately desert and the hot arid conditions are excellent for preservation of various archaeological remains. Thus, there are more and more obvious sites available for excavation. The irony is, of course, that even in Egypt, buildings of daily life, like houses, administrative buildings, even palaces, tended to be constructed of mudbrick, not stone, and settlements tended to be close to the river. All of these things taken together mean that we do not know nearly so much about Egyptian settlements as we do about Egyptian tombs and temples.
Also, there is a bias toward the study of Egypt and North Africa for a variety of reasons. The majority of archaeology in the past and even today is undertaken by people of European origin and tends to reflect their particular interests. For a long period of history, sub-Saharan Africa was regarded as "uncivilized" and not necessarily worth study. The terrain can be difficult, finding sites can be very challenging, and so little research was done. Political concerns also played a role - archaeologists who did not agree with the political lines of people in power often found it difficult if not impossible to work(for example, the controversy over Great Zimbabwe when the current nation of Zimbabwe was called Rhodesia and white supremacists did not want the construction of Great Zimbabwe to be associated with black Africans).
The current unrest in many African nations continues to discourage the practice of archaeology in many parts of Africa and African nations tend to have larger concerns than study of archaeological heritage. As more Africans begin to develop an interest in archaeology (a trend that has already begun), as conditions stabilize to allow the pursuit of archaeological projects, and as more and more sophisticated methods of site location, particularly remote sensing applications are developed and made available, I suspect we will see some wonderful, surprising developments in the broader field of African archaeology and a great deal of new information about the development of complex societies in sub-Saharan Africa.