I believe it was the Stock Market Crash of 1929
The Lost Cause of the Confederacy, or simply the Lost Cause, is an American pseudo-historical,[1][2] negationist ideology that advocates the belief that the cause of the Confederate States during the American Civil War was heroic, just, and not centered on slavery.[3] This ideology has furthered the belief that slavery was moral, because the enslaved were happy, even grateful, and it also brought economic prosperity. The notion was used to perpetuate racism and racist power structures during the Jim Crow era in the American South.[4] It emphasizes the supposed chivalric virtues of the antebellum South. It thus views the war as a struggle primarily waged to save the Southern way of life[5] and to protect "states' rights", especially the right to secede from the Union. It casts that attempt as faced with "overwhelming Northern aggression". It simultaneously minimizes or completely denies the central role of slavery and white supremacy in the build-up to, and outbreak of, the war.[4]
