In the U.S. criminal justice system, Black Americans are more likely to be arrested and spend time in prison than others. However, the literature on policing and the criminal justice system emphasizes the behavior of individuals (e.g., racially biased police officers, probation officers or judges who are responsible for disparities in arrests, parole decisions or sentencing), rather than the effects of criminal justice policies (i.e., the rules that jurisdictions use to implement the law). Economist Ellora Derenoncourt and her collaborators will study the development of criminal justice policies adopted after the Great Migration (1940-1970) when millions of Black Americans left the rural south in search of greater opportunity in northern U.S. cities. Yet, incarceration rates in these northern destinations increased as black migration increased. The investigators will analyze the extent to which modern policing developed in response to the growth of Black communities in northern and western states and the consequences of this policy development for racial gaps in income, employment and intergenerational mobility.