What movement of people to bring a sense of unity of language to much of africa?

Bantu migrations helped bring unity of language to much of Africa.

The Bantu tribe migrated from the south of West Africa to the Sub-Saharan countries excluding South Africa and Namibia. The tribe also dominated countries such as Kenya, Nigeria, etc. As they were spreading out to these countries, they introduced new skill and technology for crop-farming, harvesting and using the iron for making tools.  

The Bantu migration to African countries introduced language which is evident today due to the similarity of languages in most of these countries. Up to 500 languages spoken in these regions, is attributed to the Pro-Bantu language.