FIFTY years ago, Shaw, a historically black neighbourhood ten blocks from the White House, was ablaze. The spark had been lit nearly 900 miles away. On April 4th 1968 Martin Luther King had been assassinated in Memphis, Tennessee. After the civil-rights leader’s murder, riots gripped more than 100 cities. Shaw, a centre of black culture whose Howard Theatre had fostered the careers of Ella Fitzgerald and Duke Ellington, burned like a city at war. By the riots’ end 1,200 buildings were damaged and 12 people were dead. And more than life and property were imperilled. The whole project of civil rights seemed to be on trial. The year before, calls to tear down race barriers had both stoked, and been hurt by, massive riots in black quarters of Detroit and Newark.

In February 1968 the Kerner Commission, created by President Lyndon Johnson to investigate race riots, had warned that “our nation is moving toward two societies, one black and one white—separate and unequal”. The commission described a country blighted by ghettos, neighbourhoods in which too many citizens were trapped by poverty and race.

“White society is deeply implicated in the ghetto,” the commission wrote. “White institutions created it, white institutions maintain it, and white society condones it.” The report had identified a truth known to many Americans, even if it was not always acknowledged. Even as legal barriers of segregation were dismantled, in cities and towns across the country, and not just in the Deep South, residents knew that a certain street, a railway track or other barrier, marked a colour line. Some barriers were enforced with lethal violence, as mobs attacked black professionals who had moved into white neighbourhoods. Others were maintained with genteel discretion, even after the Supreme Court in 1948 abolished covenants that bound white property owners to rent or sell within their race (sometimes they were also told to shun Jews). The Fair Housing Act of 1968 set out to abolish “red lines”, racial boundaries which some mortgage lenders and estate agents worked hard to maintain.

Half a century after the flames were extinguished in Shaw, America remains an unequal place. To focus on one troubling fact, too many ghettos live on. Worse, the data show ghettos becoming increasingly concentrated sinks of poverty, disproportionately affecting non-whites. The bleakest charge, heard in political speeches, in academic discourse and from community campaigners, is that American schools and neighbourhoods are resegregating along racial lines, in mockery of King’s legacy.

The reality, however, is more nuanced. Since 2000, there has been an explosion in the number of Americans living in neighbourhoods of concentrated poverty, where more than 40% of the population live on an income below the federal poverty level, currently $25,100 for a family of four. According to Paul Jargowsky, a professor at Rutgers University, nearly 14m Americans live in such neighbourhoods, compared with 7m in 2000.

Those unhappy numbers cannot be untangled from questions of race and ethnicity: 25% of the black poor live in ghetto neighbourhoods, as do 17% of poor Hispanics. Among poor whites, just 8% live in areas of concentrated poverty (though those numbers are complicated by the difficulty of comparing rural and urban deprivation). Children raised in ghettos must contend with higher crime rates and schools that do not ready them for the world of work, or even keep them safe. Such places are less healthy, with substantially higher rates of lead poisoning, depression, teenage pregnancy and premature death.

A dream unfulfilled

Talk of two Americas—one for whites and the other for non-whites—is re-emerging. Fred Harris is the lone surviving member of the Kerner Commission. He has declared America at risk of descending into fresh disorder and chaos, because “housing and schools have been rapidly resegregating, locking too many African-Americans and Latinos into slums and their children into inferior schools”.

This is in part an argument about statistical methods. Some statistics on racial and ethnic integration in schools do indeed look alarming. One oft-cited measure involves the percentage of black pupils who attend majority-white schools. That number was, in effect, zero before the civil-rights era, then shot up dramatically during the era of court-mandated integration plans. Those were hard-fought gains, and not just in the Deep South. In 1974 white Bostonians violently protested against a court-ordered integration scheme, hurling bottles, eggs and bricks at buses carrying black children. In recent years, however, the proportion of black pupils at mostly white schools has dropped steadily.

Yet context matters. In 1970, 80% of school-age children were white, according to census data. Today, mostly because of growth in the Hispanic population, just 52% are. That means fewer majority-white schools to attend. In New York City’s public schools, just 15% of pupils are white.

To find routes out of the ghetto, America will need accurate maps. Tell a demographer the number of black children, rich whites or other group in a city, school district or area, and they can calculate a “dissimilarity index” which measures whether that group is clustered in certain neighbourhoods or schools, or spread evenly. An index of 100 signals the most extreme clustering possible, and an index of zero a perfectly even distribution.

Taken soon after Martin Luther King’s death, the 1970 census showed an America almost completely segregated by race. Across the country’s 60 largest cities, the dissimilarity index for black residents was 93. Put another way, 93% of blacks would have had to move districts in order to be evenly distributed, citywide. School districts were not much better. In 1970, 80% of elementary-age pupils would have had to move to ensure integration. In the four decades since, those numbers show more, not less, racial mixing. For schools the dissimilarity index has fallen to 47. Among cities, it has also dropped to 70—still high, but not increasing.

Ghettos without guards

Northern and midwestern cities are home to strikingly persistent ghettos. The cities that are the most racially segregated are not in the conservative Deep South. They are such Democratic-voting bastions as Philadelphia, Chicago, Detroit and New York (see chart). In 1970 black-white dissimilarity in New York City was 86—at the time of the last census, in 2010, it was 84. Ghettos and colour lines have been so hardy in such cities that their names inspire songs, films and fashion: the South Side, 8 Mile and the South Bronx.

Today middle-class blacks, Hispanics and other minorities can and do move away from ghettos and deprived barrios. Roughly once a decade, the federal Department of Housing and Urban Development (HUD) looks for racial discrimination through paired testing. White and black actors are given matching fictional identities before seeking flats and then comparing notes. The most recent, in 2012, showed that outright racial discrimination has dropped close to zero, though subtler differences (such as the number of homes shown to prospective residents) persist.

Less happily, income segregation is on the rise, in both cities and schools. Historical racism and modern-day inequality cannot be neatly separated. Forcing generations of black Americans into bad housing, inferior schools and unpopular jobs to keep them in certain neighbourhoods was an act of both racial and economic violence. Within the ghetto, crowded apartments were divided, then subdivided further. Because of artificially constricted supply, blacks paid more for poor houses. The intergenerational effects live on, even among black Americans who successfully enter the middle classes. An analysis by the Pew Research Centre in 2016 found that, including property, the median net worth of black households headed by someone with at least a bachelor’s degree was $26,300 in 2013. For households headed by white holders of college degrees, the median net worth was $301,300—11 times greater.

Segregation is not only a function of race. The poor, of whatever colour, cluster in class enclaves. The richest 10% are more likely to live among the similarly affluent. The college-educated also increasingly live among their peers, a surge driven by families with children. Wealthier families seem to be moving towards better-performing schools, while rising income inequality traps poorer families. Between 1991 and 2012, segregation of poor pupils increased by 40%. Research by Sean Reardon of Stanford University shows that the gap in achievement between rich and poor pupils is now twice as large as that between black and white ones.

But some experiments to move families from poverty-blighted neighbourhoods have worked—and have showed the terrible cost of inaction. The Moving To Opportunity scheme, sponsored by HUD, randomly assigned families to receive housing vouchers that required them to move to better areas. The benefits were, in social-science terms, astonishing. Children who moved before the age of 13 went on to have incomes 31% higher than those who remained. HUD operates a voucher scheme for poor Americans, but it does not do a good job of moving recipients to better districts. The chance goes to only a quarter of those who qualify. Waiting lists are sometimes a decade long.

The scars of racial segregation persist. Blacks have significantly higher rates of downward mobility than their white peers. They are more likely to remain in poorer areas when they have money to move. Affluent blacks still live in poorer neighbourhoods than working-class whites. The criminal-justice system is experienced very differently by whites and non-whites. But the charge that the country is resegregating along racial lines is a counsel of despair. The existence of ghettos is no longer enforced by implacable bigots. They are too hard to escape. Fifty years after King’s death, should call this generation to action.