I've tried both July and Shillington for an introductory survey in
AFrican history and I find Shillington (Kevin Shillington, History of
Africa, St. Martin's) works best, although it is not limited to
pre-colonial Africa. But it seems indispensable to supplement it with
Patrick Manning's Slavery and African Life (Cambridge) to fully
appreciate the effects of slavery and the slave trade on Africa--students
balk at all the graphs, but Manning does a good job making the arguments
clear and demonstrating the very diverse impacts at various periods.