How is it that the main economic/political ideology of the American (antebellum) South - namely, slavery - was replaced by the contemporary economic/political ideology of free-market (laissez-faire/ regulation free) capitalism?

I understand this coincides with the shift from Southern Democrats to the current stronghold of Republicanism... but how did that ideological change take place?

I've done some historical work about post-Civil War social memory (at the M.A. level) so there is no need to ELI5, but if it makes it easier, feel free. This doesn't relate directly to my work, I've just been watching a lecture about post-war Atlanta on CSPAN this morning. Thanks in advance!