Lisa McGirr is a professor of history at Harvard and the author of “Suburban Warriors: The Origins of the New American Right.”

In many of America’s once pristine suburbs, harbingers of inner-city blight — overgrown lots, boarded up windows, abandoned residences — are the new eyesores. From the Midwestern rust-belt to the burst housing bubbles of Nevada, California and Florida, even in small pockets of still affluent regions like Du Page County, Ill., the nation’s soaring poverty rates are visibly reclaiming last century’s triumphal “crabgrass frontier.” In well-heeled Illinois towns like Glen Ellyn and Elgin, unkempt, weedy lawns blot the formerly manicured, uniform and tidy landscape.

The Brookings Institution reported two years ago that “by 2008 suburbs were home to the largest and fastest growing poor population in the country.” In the previous eight years, major metropolitan suburbs had seen poverty rates climb by 25 percent, almost five times faster than cities. Nationwide, 55 percent of the poor living in the nation’s metropolitan regions lived in suburbs.

To add insult to injury, a new measure to calculate poverty — introduced by the Census Bureau just last year — darkens an already bleak picture: nationally, 51 million households had incomes less than 50 percent above the official poverty line, and nearly half of these households were in suburbs.

Why is poverty soaring in the suburbs? Part of the answer, according to the Brookings Institution, is simple demographics: More Americans live in the suburbs, so there are more poor people there, too. But the recent downturn has also had an outsize impact on suburbs, with the decline in certain categories of jobs and an end to the housing boom that drew many urbanites and immigrants to the suburbs in the first place....