The Democrats maintained the institution slavery
How did the republications fix the Democratic problem in the south? good question
It was done over time
It could only happen if the South would begin to move away from Democratic racism and to the republicans. This Southern strategy to remove the Democratic institutional racism took over 40 years and is still happening. basically it only happened because the racist Democrats all died eventally...Very few switched
How do you measure if it was successful, look at the amount of Blacks leaving the democratic segregation of Northern democratic cities to move to the free republican south