A copy of a Koran inside the An-Nasr Mosque on Jan. 13, 2014, in Vilvoorde, Belgium. (Virginie Nguyen Hoang for The Washington Post)

Even before bombings killed dozens in Brussels on Tuesday, Belgium was in the spotlight for the wrong reasons.

The trail from an Islamic State attack in Paris last year led to the Belgian capital. The suspected mastermind of the massacres then was a Belgian national. Numerous reporters beat Brussels's streets; many invariably penned long pieces about the woes of Molenbeek, the Brussels municipality that appeared to be ground zero for Islamist radicalization in the country.

That focus appears to be tragically warranted. Authorities have now suggested that Salah Abdeslam — the only surviving Paris assailant, who was seized by authorities last week — may have possibly had a hand in Tuesday's bombings. The attacks, my colleagues report, are being described as the worst on Belgian soil since World War II.

“What we had feared has happened,” Belgian Prime Minister Charles Michel said. “This is a black moment for our country.”

"We can say that there's a high level of threat throughout Europe," French Interior Minister Bernard Cazeneuve told television station France 2. "We have been hit, today it's the Belgians, and other capitals could be" attacked, too.

A statement publicized by a website linked to the Islamic State hailed "the soldiers of the caliphate" who carried out the attacks on the main airport in Brussels — the de facto capital of the European Union — and the metro. It also warned "the crusader state" of Belgium and its like-minded allies of "dark days ahead." According to one count, the Islamic State has killed more than 1,200 people outside Iraq and Syria — where the group controls large swaths of territory — since 2014.

Of all the countries in the West, Belgium has produced the greatest number of foreign jihadists per capita who are fighting in Syria. The actual figure, according to researchers, is variously estimated at 470 to 553. Roughly a third of those who left to fight in Iraq and Syria have returned; many have not faced prosecution, with authorities struggling to prove that the fighters joined violent organizations such as the Islamic State, which is also known as ISIS and ISIL.

According to an analysis by the Royal Institute for International Relations, or Egmont, a Brussels-based think tank, the majority of Belgian jihadists are young (ages 20 to 24), have lower-than-average education levels and are mostly of Moroccan heritage.

The prevalence of Islamist extremism in Belgium predates the incidents of the past year, as well as the advent of the Islamic State. And this is not the first time an Islamic State proxy has struck on Belgian soil: In May 2014, a gun-wielding French national who had spent time in Syria killed four people in the Jewish Museum of Brussels.

The root causes of radicalization are largely familiar: high unemployment, marginalization, discrimination and a sense of alienation from the wider society.

BuzzFeed's Joshua Hersh spent time in Molenbeek and came away with this picture of a downtrodden, disgruntled community:

Unlike the infamous banlieues of Paris — the rundown high-rise suburbs that symbolize France’s failure to integrate its own Muslim immigrant residents — Molenbeek is practically in the middle of Brussels; it’s just two metro stops west of the central train station. Still, Molenbeek can feel deeply isolated. The immigrants of Brussels, most of them Muslim and of North African descent, are highly concentrated there — the schools they attend, shunned by white Belgian families, are disparagingly referred to as “concentration schools,” after the high percentage of immigrants enrolled, and the poor conditions. “I didn’t believe it was this bad when I first started,” said a teacher who works at a mostly immigrant school near Molenbeek. “The schools, all they do is accentuate the problems the students face in their daily lives.”

Moreover, as my colleague Michael Birnbaum reported, Belgium's pronounced linguistic divisions between Dutch-speaking Flanders, the largely French-speaking city of Brussels and the region of Wallonia to the south have made it difficult for some immigrant groups to assimilate. This is particularly true of those living in Flanders, where far-right Flemish nationalist parties hold real sway and inveigh against the dangers of Islam.

“The Islamic State is giving them what the Belgian government can’t give them — identity, structure,” Montasser AlDe’emeh of the University of Antwerp told Birnbaum. “They don’t feel Moroccan or Belgian. They don’t feel part of either society.”

According to the Egmont report, the current crop of Belgian extremists are significantly younger than earlier generations, which went off to join the ranks of al-Qaeda and other fundamentalist groups. That radicalization is driven less by religious fervor than by more local factors, and it is shaped also by ties to gangs and other criminal activity:

Their acquaintance with religious thought is undoubtedly more shallow and superficial than their predecessors’, as is their acquaintance with international politics. Geopolitics is less important to them than it once was to their predecessors, who felt motivated by the struggle against the superpowers. Injustice was often a starting point with their predecessors’ journey towards extremism and terrorism. This has now largely been overshadowed by personal estrangement and motives as the primary engines of their journey

The report goes on to cite a top Belgian police official, who said the country in the past had been "mostly dealing with ‘radical Islamists’ — individuals radicalized toward violence by an extremist interpretation of Islam — but now we’re increasingly dealing with what are best described as ‘Islamized radicals.’"

At a security conference this weekend, Belgian Foreign Minister Didier Reynders had emphasized the "many links between the so-called terrorist and the criminals," suggesting militants, such as Abdeslam, exploited the same infrastructure used by local gangs and syndicates.

The nihilistic allure of the Islamic State, combined with its sophisticated recruitment networks as well as communities of support elsewhere, led to a period when upwards of a dozen Belgian nationals a month were leaving the country to journey to Syria. That rate of recruitment has dwindled after government crackdowns, but top officials, including the prime minister, have acknowledged that the situation has slipped out of control.

No one is entirely sure of the number of potential jihadists who have returned from the front lines in Syria and Iraq. "Recruitment continues — at a much lower level than we were used to, for example, two years ago — but, yes, it continues," Belgian Interior Minister Jan Jambon told CNN, gesturing to the ease with which militants can operate online. "It is difficult to find the people that are [responsible] — you can do it in a small room in every house."

The difficulty of the challenge mirrors the complexity of its causes. The Islamic State's plots in Europe have largely hit soft targets, a sign of the group's willingness to sow terror wherever it can. Yet heavy-handed policing methods risk antagonizing and stigmatizing a whole community, and deepening radicalization.

The Egmont report urges local authorities to clamp down on departures to Syria, invest in better community policing and separate "the discussion on Islam in Europe from deradicalization initiatives."

Europe "has created the conditions for the resentment that drives the terrorists, but the vast majority of people in those conditions do not resort to terrorism," said Cas Mudde, an associate professor at the School of Public and International Affairs at the University of Georgia. "But it also doesn’t mean that simply destroying foreign terrorist threats like ISIS would get rid of the ‘Jihadi threat’ in Europe."

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