The movement of many different tribes from west africa to the south and east is know as

Bantu expansion

Explanation: The Bantu expansion was a major series of migrations of the original Proto-Bantu-speaking group, which spread from an original nucleus around West-Central Africa across much of sub-Saharan Africa. In the process, the Proto-Bantu-speaking settlers displaced or absorbed pre-existing hunter-gatherer and pastoralist groups that they encountered.  The primary evidence for this expansion is linguistic – a great many of the languages which are spoken across Sub-Equatorial Africa are remarkably similar to each other, suggesting the common cultural origin of their original speakers. The linguistic core of the Bantu languages, which comprise a branch of the Niger–Congo family, was located in the adjoining regions of Cameroon and Nigeria. However, attempts to trace the exact route of the expansion, to correlate it with archaeological evidence and genetic evidence, have not been conclusive; thus although the expansion is widely accepted as having taken place, many aspects of it remain in doubt or are highly contested.

an economic reason that the south needed a reconstruction plan is that plantations, factories, and other businesses were destroyed during the war.