I do not want to get into a long political discourse here, but perhaps you would like to read this article from the History Channel - https://www.history.com/news/how-the-party-of-lincoln-won-over-the-once-democratic-south This paragraph from the text captures the beginning of the change in 1948. "These defectors, known as the “Dixiecrats,” held a separate convention in Birmingham, Alabama. There, they nominated South Carolina Governor Strom Thurmond, a staunch opposer of civil rights, to run for president on their “States’ Rights” ticket. Although Thurmond lost the election to Truman, he still won over a million popular votes."