Map 18 (this page) shows the extent of slavery by plotting the percentage of the population that were slaves across U.S. counties in 1840. It is apparent that slavery was dominant in the South with some counties, for example, along the Mississippi River having as much as 95 percent of the population slaves. Map 19(this page) then shows one of the consequences of this, the proportion of the labor force working in manufacturing in 1880. Though this was not high anywhere by twentieth-century standards, there are marked differences between the North and the South. In much of the Northeast, more than 10 percent of the labor force worked in manufacturing. In contrast in much of the South, particularly the areas with heavy concentrations of slaves, the proportion was basically zero