The History of African-American Vernacular English
African American English (AAE) originated from contact between Africans and Whites during slavery. The trajectory of slavery in the United States was different from that in the Caribbean, but in areas where population ratios and time frames were most like those in the Caribbean, a creole language, Gullah, emerged. In other areas, various degrees of creolization may have taken place. As a result, early AAE was not monolithic and included some regional variation. In recordings with former slaves and African Americans born during the last half of the 19th century, the reflexes of AAE’s origins appear in features that have strong parallels with Gullah and Caribbean creoles, including zero copula/auxiliary, monophthongal /e/ and /o/, fully back vowels, and non-front onsets of /au/.
As African Americans moved from slavery into farm tenancy, features emerged in AAE that were shared with Southern White vernaculars. These include grammatical forms such as yall and fixin’ to and phonological features like monophthongal /ai/ and the pin/pen merger. However, even as shared features emerged, AAE maintained its distinctiveness by typically not participating in the Southern Shift that affected vowels in Southern White vernaculars. Developments during the Great Migration in the 20th century enhanced AAE’s distinctiveness. During the Great Migration such well-known features as durative/habitual be, ain’t for didn’t, and had + past as a simple past became widespread.
AAE, then, is a product both of its unique heritage and the historical and demographic processes that promoted its independent development and also of people who valued (and still value) it as a mode of communication and as an instrument for identity and solidarity.
Bailey, Guy. "The History of African-American Vernacular English." Oxford Research Encyclopedia of Linguistics. 15. Oxford University Press. https://doi.org/10.1093/acrefore/9780199384655.013.926
Oxford Research Encyclopedia of Linguistics