In the decades after World War II, as factories and mills closed and the economy that shaped the whole sprawling city until then collapsed, the “inner city” of Chicago became the place you fled, at least if you were white and had money. Between 1950 and 1990, the population of Chicago declined by 837,000 people. But in the past two decades, the city began to add residents again. No longer hog butcher or toolmaker, Chicago emerged from its long decline as a self-proclaimed “global city” — a tourist destination for the world, a player with derivatives and trade shows, a city of big transportation hubs. Between 2000 and 2010, the number of residents in the city’s central area increased by 48,000 (more than any other city center in the country), and even with tens of thousands of new condos added there before the housing crash, vacancy rates for high-end apartments currently stand near a 10-year low. Richard M. Daley, who during his 22 years as mayor did much to foster the downtown renaissance, even moved from Bridgeport, the family’s old sod on the South Side, to a new upscale development overlooking Millennium Park, which he built. The current mayor, Rahm Emanuel, has already induced 15 corporations to relocate their headquarters to Chicago. “The city is no longer a place to get on a plane and go to the coasts,” Emanuel said in May, “but a place to stay and call home.”

None of this is revelatory. It’s a thumbnail history that any Chicagoan could tell you, and it’s similar to the trajectory of any number of American cities. The conundrum that exists in Chicago, though, is what happens to the “something else beyond” now that the center is prospering. For the people trying to make their lives in the areas that J. R. and his fellow activists are trying to save, the question is not at all a theoretical one. The way many of them see it, they’re being sacrificed so that the city can be reborn.

In these outlying communities, as well, the residents with the means to leave often have, compounding the problems of concentrated poverty. From 2000 to 2010, while affluent whites were migrating back to downtown, Chicago’s African-American population fell by 181,000, an astounding 17 percent drop. Many of them decamped for the south and west suburbs as well as the relative safety and higher living standards of the actual South. The foreclosure crisis then blew through and removed a lot of the remaining homeowners and wealth. It was hard for people on the South Side and the West Side not to see evidence of an engineered shrinkage, a strategy to starve derelict communities of resources, thus bringing about their further depopulation and return to nature. Over the past decade and half, Chicago razed all 82 of its troubled housing project high-rises, the biggest civic redesign since urban renewal placed the massive tower-and-garden developments there in the first place. The towers had become warehouses for the most disadvantaged, symbols of urban decay and the failures of government to reverse this slide. Getting rid of the projects meant that areas near the expanding zone of affluence were cleared of blight. They were also cleared of many of their former inhabitants.

Chicago no longer has the money for big urban renewal projects. Earlier this year, Emanuel did announce an initiative that will couple public and private investment to try to revive several communities that possess — or are at least on the edge of — some existing economic development. In Pullman, on the far South Side, for instance, a Walmart is expected to anchor a 180-acre mixed-use facility. The mayor described how these pockets of activity could become larger, link up and eventually form corridors that lead from, say, the South Loop, through Bronzeville and Hyde Park. But most city plans appear to be focused on land use and stabilization, not development. The city is escalating a program that allowed homeowners to acquire adjoining vacant lots, leaving them with expansive grassy estates. It is promoting urban agriculture and looking to turn empty rail lines and other industrial sites into recreation trails and natural drainage systems. At the same time, the city spent $14 million last year to knock down 736 vacant buildings, including 270 abandoned homes that the Police Department identified as shelters for gangs and other criminal activity.

And then there’s Emanuel’s plan to close 50 schools, almost all of them in the same black and Latino neighborhoods battered by the foreclosures and a recent spike in homicides. The closures weren’t a matter of downsizing, Emanuel has said in the face of intense protests and criticism, but of trading up academically; he has pledged $155 million for upgrades at the “welcoming schools.” Others were worried more about the long-term consequences of these actions. “It’s a slow death once you take the schools out of these communities,” Brad Hunt, an urban historian and co-author of the recent book “Planning Chicago,” told me. “No one is talking shrinkage, even though that’s what we’re doing. In Chicago, that’s not the image we have of our city.”

Before turning to activism full time, J. R. still shared a name with his father, everyone calling him Junior. It seemed too small to him. He said his father was a C.I.A. operative, as well as a gunrunner and drug kingpin at the Cabrini-Green housing complex. His mother, Marlene McIntosh, was a former Black Panther and community organizer who moved the family around a lot. J. R. stayed on the South Side, in the Robert Taylor Homes — once the world’s largest housing project before the city tore it down — and at Cabrini-Green, the Hilliard Homes, the Henry Horner Homes, an apartment on the West Side, another place out in Waukegan and also in the south suburb of Dolton, just outside the Chicago city limits. He left the suburbs before his senior year of high school, moving in with a sister back at Cabrini-Green.

He had his first child there that summer. (The first of 10, a number that city officials, I’ve found, like to mention with a derisive raising of an eyebrow.) Cabrini-Green was then a 23-tower, 3,600-unit island of black abject poverty amid a steadily encroaching sea of white affluence. Located just blocks from the ritzy Gold Coast, the North Side development offered an unusual mix of isolation and access, and many residents were deeply attached to their home, tragic as it was. The towers clutched around J. R.’s high-rise were each controlled by a different gang, and the blacktop between them was known as the killing fields. On days when rumors spread of a retaliatory sniping, mothers would rush to the schools to collect their children, the teachers left standing before emptied classrooms. But J. R. could also point to the field where he played softball and the path along the river where he walked with girlfriends. He had family in nearly every building of the 70-acre project. Cabrini was his home, his identity, and tearing it down felt like taking an eraser to his past.