For the most part, before the war, blackness marked one as a slave. Afterward, it marked one as the lowest of laborers, relegated to sharecropping and domestic work, excluded from the mounting ranks of industrial labor. “With the coming of industry and the factory system, the social code which made manual labor a degrading factor was no longer of binding force,” the historian Charles H. Wesley wrote in his 1927 book “Negro Labor in the United States, 1850-1925.” “Work in the factories was honorable and it was to be considered the particular task of white workers.”

Which is to say that, as it developed in the United States, industrial capitalism retained a caste system with whites as the dominant social group. This wasn’t just a matter of prejudice. As it did under slavery, race under industrial capitalism structured one’s relationship to both production and personhood. Whiteness, the philosopher Charles W. Mills notes, underwrote “the division of labor and the allocation of resources, with correspondingly enhanced socioeconomic life chances for one’s white self and one’s white children.”

It’s not that life was particularly good for white workers, but that blacks faced additional challenges, from the denial of formal political rights to social exclusion and widespread, state-sanctioned violence. If they lived in cities, blacks were relegated to the least sanitary neighborhoods with the most substandard housing; if they had a skill or knew a craft, they were excluded from the guilds and unions that would have given them a path to employment; if they possessed a formal education, they were barred from most middle-class professions.

The overrepresentation of blacks in institutions like the Postal Service is a direct legacy of this exclusion. Postal work was, historically, one of the few stable jobs available to blacks. “For years the post office had commonly been considered a ‘safe’ job for blacks because of exclusion by both white capital and white labor in the private sector,” the historian Philip F. Rubio explains in “There’s Always Work at the Post Office: African-American Postal Workers and the Fight for Jobs, Justice, and Equality.”

By the time we reach the New Deal era, the racial differentiation of capitalist inequality — divided labor markets, wide racial disparities in employment, income and education — was part of the pattern of American life, even in the midst of the Depression. And as policymakers in Washington worked to address the crisis, they built on that foundation and deepened those disparities, sometimes by accident, but often — because of direct pressure from the white South and its lawmakers — by design.