Competition in the promised land

"In the mid-twentieth century, relative black wage growth in the North lagged behind the Jim Crow South. Inter-regional migration may explain this trend. Four million black southerners moved North from 1940 to 1970, more than doubling the northern black population. Black migrants will exert more competitive pressure on black wages if blacks and whites are imperfect substitutes. I use variation in the relative black-white migrant flows across skill groups to estimate the elasticity of substitution by race in the northern economy. I then calculate a counterfactual rate of black-white wage convergence in the North in the absence of southern migration. Migration slowed the pace of northern convergence by 50 percent, more than accounting for the regional gap. Ongoing migration appears to have been an impediment to black economic assimilation in the urban North"--National Bureau of Economic Research web site.