
This was an intentional and systematic rewriting of history carried out by confederate descendants, particularly the United Daughters of the Confederacy. The idea that the Civil War was simply about states rights stems from this injection of propaganda across the American education system (not just the south)
You cut to today, and the areas with the most slavery still have large black populations, but now those black people can vote. And the rivers and ports that allowed cotton export are now cities which tend to be more progressive politically. Meanwhile the white communities up in the mountains have gravitated towards the tying of social conservatism with the confederacy, even though before they were anti-confederate.