That is a new paper (pdf) by Avidit Acharya, Matthew Blackwell, and Maya Sen, here is the abstract:
We show that contemporary differences in political attitudes across counties in the American South trace their origins back to the influence of slavery’sprevalence more than 150 years ago. Whites who currently live in Southern counties that had high shares of slaves population in 1860 are less likely to identify as Democrat, more likely to oppose affirmative action policies, and more likely to express racial resentment toward blacks. These results are robust to accounting for a variety of attributes, including contemporary shares of black population, urban-rural differences, and Civil War destruction. Moreover, the results strengthen when we instrument for the prevalence of slavery using measures of the agricultural suitability to grow cotton. To explain our results, we offer a theory in which political and racial attitudes were shaped historically by the incentives of Southern whites to propagate racist institutions and norms in areas like the “Black Belt” that had high shares of recently emancipated slaves in the decades after 1865. We argue that these attitudes have, to some degree, been passed down locally from one generation to the next.