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.

As public resources were desegregated in American cities, communities increasingly found ways to privatize them. In McKinney, the black teens were not using a public pool. They were swimming, rather, in the communal pool of a private community in the predominantly white part of town where civic resources like parks and pools are funded directly by homeowners. McKinney has three public pools, Appelbaum points out, but none of them are in this part of town.

We don't know what precisely happened before and after the moments captured on video. But for these black teens, the issue may not have been so much — or solely — their behavior, as their presence at a pool where residents who called the police suspected they did not belong.

The incident exposes the unspoken logic of gated resources: They are meant to give residents control over who's in the community that can use communal goods. Private community swimming pools do a good job at this (in this McKinney community, residents are allotted a few guest passes a piece). Really private pools — in the fenced back yards of individual homes — achieve this even more effectively. Here's an instructive history lesson from Appelbaum:

In Marshall, Texas, for example, in 1957, a young man backed by the NAACP sued to force the integration of a brand-new swimming pool. When the judge made it clear the city would lose, citizens voted 1,758-89 to have the city sell all of its recreational facilities rather than integrate them. The pool was sold to a local Lions’ Club, which was able to operate it as a whites-only private facility.
The decisions of other communities were rarely so transparent, but the trend was unmistakable. Before 1950, Americans went swimming as often as they went to the movies, but they did so in public pools. There were relatively few club pools, and private pools were markers of extraordinary wealth. Over the next half-century, though, the number of private in-ground pools increased from roughly 2,500 to more than four million.

This exact same phenomenon has surfaced in many forms well beyond swimming pools. Americans have replaced — or, rather, withdrawn from — many of the public spaces and shared resources that were prominent in communities decades ago. And so private schools take the place of public ones, individually owned cars replace mass transit, secluded yards supplant public parks. Communal plazas of all kinds become "privately owned public spaces" where companies and property owners control who can access them.

In another example from McKinney, a private security officer was among those who called police to intervene.

Excessive police use of force is in and of itself a problem, one increasingly recognized by politicians from both political parties. Here, though, as with so many of these stories lately, much more — the way we design communities and divide their resources with race and class quietly in mind — is implicated, too.