In Paris, the suburbs — les banlieues — evoke a world more akin to the inner-city in America. The drab, concrete high-rise housing for the poor is located there. Crime is high. Work is scarce, and young people who can't find it linger on the streets. As in America, too, poverty and race are intertwined: The housing projects and Halal butcher shops there are full of immigrant families, Arabic-speaking men, the children of migrants who came looking for work from the former French colonies in Africa.

These places exist apart from the rest of Paris, even France, and — as is occurring across major European cities — the distance between the two is hardening. Socioeconomic segregation in Europe is growing worse, according to a large study recently published by researchers across the continent. "The potential estrangement that may be the result of such contrasts," they warned, "might be dynamite under the social stability of our future cities."

Their book, "Socio-Economic Segregation in European Capital Cities," was published in August, before the homegrown terrorist attacks in Paris last month, before we learned that several of the attackers came from the Paris banlieues and that others lived in the troubled Molenbeek quarter of Brussels ("There is almost always a link with Molenbeek," Belgium's prime minister admitted). The researchers' warning was prescient for this moment, as Europe considers what to do with the kinds of cut off and impoverished communities that keep turning up ties to violence and that also gave way to riots outside Paris in 2005London in 2011 and Stockholm in 2013.

"Segregation in Europe is reaching U.S. levels," says Maarten van Ham, one of the book's editors and a professor of urban renewal at Delft University of Technology in the Netherlands and the University of St. Andrews in Scotland. His data reflect segregation by income and occupation, but as Europe has grown more diverse through immigration, these divides map onto places like the banlieues and Molenbeek that are also heavily minority and Muslim.

"And this is a complete shock," he adds of the growing problem, "for not just national governments, but also the European Commission."

Segregation, Europeans thought, was an American problem. Europe was always supposed to be more equal.

According to the study, though, segregation rose in the 2000s across countries in Europe with varying politics, social safety nets and pubic housing systems. It rose in Sweden, which didn't see its first major wave of immigration until the 1990s. It rose in Estonia, a Soviet country just a generation ago. It rose in Spain, where more than three-quarters of households own their own homes.

The trend, fed by a shifting economy, rising immigration and retreating welfare states, bodes badly for Europe's troubles integrating newcomers, Muslim minorities and young adults who feel excluded from society. And it shows the limits of the more generous — but fraying — European social safety net, which has provided housing for the immigrant poor but not necessarily opportunity.

Where segregation in the United States stems from historic patterns we've never fully addressed — patterns dating to slavery and Jim Crow, that cemented white suburbs and black inner cities  in Europe it's arising from more recent forces to which the continent is still struggling to respond.

"It’s a different history," van Ham says. "It’s a completely different story than the U.S. story."

The American example, though, is cited as a kind of worst-case scenario in Europe. Policymakers and politicians reacting to the book have asked van Ham if European communities will turn into American-style ghettoes. In French and Dutch and German, people use an odd anglicism — "no-go" areas — to describe what Americans might call "bad neighborhoods," as if the very concept were imported from abroad like fast food.

"When politicians in Europe talk about 'no-go areas,' they often refer to what they think is a U.S. situation," van Ham says. The phrase conjures, he explains, "very high levels of inequality, racial inequality, racial segregation. That’s the image people have of the U.S. And a lot of people are worried that's the direction Europe will go."

European segregation, though, has its own added complications bound up in immigration (as black segregation in the U.S. does not) and religion (as most immigration in the U.S. does not). Many of the North African and Turkish laborers who temporarily came for low-skilled work in Europe in the 1960s and early 1970s settled in the brutalist apartment complexes that had been built as desirable workforce housing (as American public housing once was). Within a decade, van Ham says, those projects became enclaves for low-income ethnic minorities.

They've remained that way since, as temporary workers stayed permanently, many later bringing over their families. Other European countries like Sweden later became havens for asylum seekers from war-torn countries like Yugoslavia, Iraq and Syria. But there, too, refugees ended up in the cheapest housing on the outskirts of town, isolated from jobs.

"You can be very open and generous to people, but once they’re in the country, yes they’re getting housing, and they have enough for food, but no investments are made in these people," van Ham says. "If you arrived 10 years ago in Sweden, and after 10 years you still don’t have a job, you still don't speak Swedish, you still don’t have Swedish friends, you apply for jobs and they discriminate against you, and the next generation — the children — are not getting opportunities, this is one of the main causes of riots."

In May 2013, the immigrant-heavy northern suburbs of Stockholm — where youth unemployment runs high — erupted in five days of riots. Van Ham fears that the same will eventually happen in the Netherlands, where local governments are preparing now to house an influx of refugees in tents and makeshift camps.

European countries that have historically been good at investing in large public works projects — "in stones," as Van Ham says — have had a much harder time investing in people. And among those people, the distinctions between citizenship and foreignness have become fuzzy; citizenship doesn't guarantee acceptance, and native-born, second-generation children can be seen as "foreign" anyway. In many ways, it's true that the neighborhoods where they grow up remain foreign from the rest of society, a fact buttressed by segregation.

"Now, in the last 10 years, you increasingly see philosophers and politicians talking about the 'bankruptcy of the multicultural society,'" van Ham says. "It hasn’t worked. How can you have third-generation Moroccans who still don’t speak the language, who still don't go to the university?

"In Belgium now, you see Molenbeek."

After the Paris attacks, you hear politicians equating Syrian refugees with terrorists.

Of course, many of those refugees are fleeing the same terrorists Europeans fear. "But it’s a fact that they are Muslims," van Ham says. "It’s a fact that they will live in our cities, it’s a fact that they will have low incomes, and they will live in the cheapest accommodation available. This will lead to more segregation. And it will lead to more tension."