The Bantu Expansion
Over roughly three thousand years, farming peoples speaking related languages moved out of what is now Cameroon and Nigeria and spread across most of Africa south of the Sahara, carrying yams, cattle, and iron. They did not march; they drifted, generation by generation, clearing forest and settling. The evidence is written in language: some five hundred Bantu tongues, from Swahili to Zulu to Shona, are related closely enough that linguists can reconstruct the parent they descend from. It is one of the largest movements of people in human history and it left no conquest to remember.
Large movements of peoples — pushed or pulled — reshape the societies they leave and the ones they enter.