I'm usually not a big believer in centralized conspiracy theories. But there really is one group most responsible for the blindness about the horrors of the African-American Diaspora. The Daughters of the Confederacy put constant pressure on textbook publishers to literally white wash the history of the south, both post and antebellum. When I was a young student, I had enough sense to know that you couldn't trust Gone with the Wind and Stephen Foster to give you the straight dope about history. But I trusted my school textbooks, which repeatedly lied to me. When I started reading other sources, especially the oral histories of surviving slaves collected by the WPA project, I realized that the Antebellum south was basically Auschwitz with mint juleps and magnolia trees.

By the way, that oral history project was created and funded by FDR's administration.