In the video — a clip that, by Monday morning, had been viewed more than 4 million times — the white officer in McKinney, Tex., pushes a black teenage girl onto the ground, unholstering his weapon as her frantic friends try to approach. The girls in the chaotic scene are all wearing bathing suits. The setting, on a Friday evening in suburban Dallas, was a community swimming pool.

As Yoni Appelbaum points out over at The Atlantic, this context is particularly freighted: For decades, swimming pools in America have been sites of racial exclusion. Many of the fights to desegregate communities and public resources in the 1950s were waged over access to swimming pools. And the way they’re used to this day still reflects a sweeping trend — more subtle in its exclusion but no less pervasive — that arose from that era.  Read more: