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... A diversity of earlier Southern dialects once existed: a consequence of the mix of English speakers from the British Isles (including largely English and Scots-Irish immigrants) who migrated to the American South in the 17th and 18th centuries, with particular 19th-century elements also borrowed from the London upper class and enslaved African-Americans.

By the 19th century, this included distinct dialects in eastern Virginia, the greater Lowcountry area surrounding Charleston, the Appalachian upcountry region, the Black Belt plantation region, and secluded Atlantic coastal and island communities.

Following the American Civil War, as the South's economy and migration patterns fundamentally transformed, so did Southern dialect trends.[11]

Over the next few decades, Southerners moved increasingly to Appalachian mill towns, to Texan farms, or out of the South entirely.[11]

The main result, further intensified by later upheavals such as the Great Depression, the Dust Bowl and perhaps World War II, is that a newer and more unified form of Southern American English consolidated, beginning around the last quarter of the 19th century, radiating outward from Texas and Appalachia through all the traditional Southern States until around World War II.[12][13]

This newer Southern dialect largely superseded the older and more diverse local Southern dialects, though it became quickly stigmatized in American popular culture.

As a result, since around the 1950s and 1960s, the notable features of this newer Southern accent have been in a gradual decline, particularly among younger and more urban Southerners, though less so among rural white Southerners. ...