Also before the Southern strategy the parties could vary massively on a regional level, for example in one county you may have had pro slavery Democrats while in the next one over you could’ve had ones who were anti-slavery and really into agricultural research.
The parties basically flip flopped starting with FDR and the new deal era.
As someone else commented this was also exacerbated later on with the “Southern strategy”
Also before the Southern strategy the parties could vary massively on a regional level, for example in one county you may have had pro slavery Democrats while in the next one over you could’ve had ones who were anti-slavery and really into agricultural research.