The first idea, advanced by the county school board, was narrow. In this view, the evil of segregation was the way it relied on racial categories. The solution was simple: stop treating children differently on the basis of race. The “freedom of choice” plan was institutionally color-blind, with the same schools available to everyone regardless of skin color. Therefore, in this view, segregation had been corrected. Because the government was no longer classifying children by race, no further action was needed.

But in Green, the Supreme Court rejected this idea of segregation. Its unanimous opinion, authored by Justice William Brennan, adopted a second, broader view. Instead of focusing on the generic question of whether racially classifying students was harmful or unfair, the Green decision described the far-reaching, systemic nature of segregation as it existed in New Kent County’s schools. In the Supreme Court’s own words: “Racial identification of the system’s schools was complete, extending not just to the composition of student bodies at the two schools, but to every facet of school operations—faculty, staff, transportation, extracurricular activities, and facilities.” The Court described this state of affairs as a “dual system” of schools, a phrase that would persist through decades of civil-rights law.

The Supreme Court was describing something more malevolent than mere racial classifications. It was recognizing the purpose of those classifications: to create a system of tiered education, akin to a caste hierarchy. And the Court was clear who was being targeted by that system: black students, who had been permanently relegated to an inferior role.

These “dual systems” were unconstitutional, the Green court said, and once they were identified, the government was required to fix what it had broken. This meant more than just getting rid of racial restrictions in schools. In the Supreme Court’s evocative language, it meant the harms of segregation had to be eliminated, “root and branch.” Justice required that any existing segregation produced by the dual system be “dismantled,” through the intentional creation of integrated schools.

School districts could select whatever means they thought would be most effective for desegregation, but they couldn’t stick with a method that didn’t work. In the case of New Kent County, the “freedom of choice” plan had proven clearly insufficient. In other places, the Supreme Court acknowledged, choice plans might prove effective, although “the general experience ... to date has been such as to indicate its ineffectiveness as a tool of desegregation.” Regardless, if choice failed, other approaches would need to be used, until integration was achieved and the harm caused by the dual system was scoured away.

An unusual aspect of the Green decision is its reliance on the history of American racial discrimination. Courts sometimes reduce the messy facts of cases to logical abstractions, which makes it easier to see idealized rules of law. Green did not do this. It identifies the narrow act of segregating a school as part of a larger system of white supremacy and racial caste. And it asserted that, to truly vindicate black Americans’ constitutional rights, the government must unmake that system, taking aggressive measures if necessary.