In The New Jim Crow, Michelle Alexander identifies two main factors which led to growing hostility among Northern whites to the Jim Crow laws. The first was the increased political power of African-Americans, manifested in the growing prominence and national prestige of the NAACP. To a considerable extent, this was due to the large-scale migration of African-American workers from the South, which not only strengthened civil rights organizations like the NAACP, but made it increasingly difficult for Northern politicians to ignore the concerns of black voters.

But the most important factor for Alexander is the impact of World War II. The United States had fought and defeated Nazi Germany, which had carried out mass atrocities on the basis of a warped ideology of racial superiority. And yet meanwhile, back home, millions of American citizens were still treated as second-class citizens on account of their race. The discrepancy between the ideals for which the United States were fighting and the condition of so many American citizens was glaring. A growing consensus emerged that it was high time for the leader of the free world to practice what it preached and get rid of the Jim Crow laws once and for all.