One thing that makes piecing together the history of sub-saharan africa easier for researchers for oral histories. oral history is

Oral history is the transmission of historical knowledge orally over time. This means that the traditions, past, and historical events of groups of peoples are not written down in text or books but instead are transmitted through oral histories over time. Oral histories are common in cultures and societies all around the world including Sub-Saharan Africa. 

Explanation:

you didn't give any answers to choose from so i can't with this but, i do know something that the mexican government would be worried about and that is the wall that donald trump is currently trying to get up.

the decreasing neutrality of the u. s. in world war i

hope this : )