From a recent read, Risa Goluboff’s The Lost Promise of Civil Rights:

The process of doctrinal distillation was particularly powerful in the years leading up to Brown. The multiplicity of the civil rights practices of the 1940s reflected both the unsettled nature of legal doctrine and the complexity of challenging a seventy-five-year-old racial and economic caste system. As lawyers transformed into legal claims attacks on the unwieldy thing called Jim Crow, they chose particular cases, particular legal theories, and particular formulations of injury that they thought legal doctrine could remedy. As a result, the civil rights case that took the definitive step towards undermining Jim Crow would, as Brown did, both embody a legal understanding of what Jim Crow was and begin to define the constitutional response to it. In so doing, that case would, as Brown also did, elide the forms of civil rights and understandings of Jim Crow that lawyers had chosen to filter out of the litigation process.

This book is a fascinating read (more so if you are a lawyer, I imagine) about how it is that we think of civil rights in the way that we do now, and how a lot of the multiple meanings of civil rights (in particular labor rights) were articulated in the years before Brown vs. Board of Education. Civil rights claims were launched on behalf of black workers by the Civil Rights Section of the DoJ as well as the NAACP, and the latter chose a very particular approach to Brown which did not build on a lot of the victories won in those earlier cases.