When two vehicle attacks left 14 dead on Thursday in Catalonia, a region known as a tourist magnet appeared to suddenly emerge as a European terrorism hotspot.

For some, however, it hardly came as a surprise.

The name of seaside resort Cambrils, where the second vehicle attack took place, is well known to many counterterrorism professionals. It is the town where two of the men accused of being key organizers of the 9/11 attacks, Ramzi Binalshibh and Mohamed Atta, met with other Islamist militants in July 2001 as part of the planning of the attacks on New York and Washington, said Fernando Reinares, director of the global terrorism program at Elcano Royal Institute in Madrid.

In 2001, Spain was already one of al-Qaeda’s first bases in western Europe. But the threat posed by the group and its associates only became fully apparent in 2004 when several explosives killed 191 people in an attack on Madrid’s commuter rail network.

Even though Spain has gone for more than a decade without any major Islamist attacks, Barcelona and its surrounding areas are still “the major radicalization hub in Spain,” said Reinares. These days, it is not al-Qaeda but the Islamic State that seeks to attract young Spaniards.

“When terrorist groups look at Europe, they see Spain as a country that used to be part of the global caliphate, and it was lost,” said Raffaello Pantucci, director of international security studies at the Royal United Services Institute, a London-based think tank. Terrorist recruiters and hate preachers have had more success in Catalonia than anywhere else in Spain in turning the mostly young men or women against their home country.

About a third of all Spanish convicted Islamist-terrorism suspects arrested between 1996 and 2013 were caught in Catalonia, according to statistics analyzed by the Elcano Royal Institute think tank. The region only accounts for about 15 percent of Spain’s overall population, however. The Madrid-based think tank also found that about half of all Spanish Salafist worship places, some of them blamed for facilitating Islamist radicalization by authorities, were located in Catalonia as well.

There are multiple explanations for the autonomous community’s extremism problem, and some of them have long been a concern to authorities in Spain and neighboring nations that fear the emergence of an Islamist militant scene that could collaborate with other extremists in southern France or northern Africa.

“There is a disproportionately high number of Spaniards who have converted to Islam — something which further intensifies existing problems as some converts want to prove to others that they truly embraced Islam and are thus more prone to violent behavior,” said Claudia Carvalho, a terrorism researcher in the Netherlands at Tilburg University, who has focused on Islamist extremism in Spain.

In recent decades, Catalonia has also seen a large influx of immigrants. The region welcomed millions of workers following an economic boom in the 1990s, but the 2008 financial crisis put a sudden end to its labor shortage.

Photos from the scene after a van plowed into a crowd in Barcelona

Medical staff members and policemen stand in a cordoned off area after a van ploughed into the crowd, injuring several persons on the Rambla in Barcelona on August 17, 2017. Police in Barcelona said they were dealing with a "terrorist attack" after a vehicle ploughed into a crowd of pedestrians on the city's famous Las Ramblas boulevard on August 17, 2017. Police were clearing the area after the incident, which has left a number of people injured. / AFP PHOTO / Josep LAGOJOSEP LAGO/AFP/Getty Images (Josep Lago)

“Much of the immigrant population in Barcelona is from Morocco, but there also are many who originally came from Pakistan or Afghanistan,” said terrorism researcher Carvalho. “The different ideologies they brought to Catalonia have made counterterrorism quite challenging,” in Catalonia, compared to countries where authorities mainly engage with one region or country of origin, she said.

Spanish intelligence officials were circulating the names of at least four suspects among their European counterparts Friday, according to a Spanish intelligence official and a European intelligence official. The four men, all holding Moroccan citizenship, ranged in age from 17 to 24, and were from the Catalan town of Ripoll, close to the French border.

By the time of the Madrid bombings in 2004, Spain already had extensive counterterrorism experience due to frequent prior attacks by the Basque separatist and left-wing ETA group, which declared a cease fire in 2006. Yet adapting existing practices to the Islamist threat has been a work in progress.

“I wouldn’t say the Catalan authorities have failed on a larger scale,” said Peter Neumann, the director of London’s International Centre for the Study of Radicalization and Political Violence (ICSR). “In fact, Catalan authorities have systematically prepared to prevent attacks in recent years.”

Such efforts were sped up after at least one major Islamist terror plot was foiled due to the help of foreign intelligence services. In 2008, authorities prevented a large-scale attack on the transportation network, planned mainly by several members of the city’s Pakistani community.

After the Madrid attack and foiled Barcelona plot, Spain “realized they were a country with a potentially big problem, and really aggressively tried to stay ahead of the problem,” said London-based counterterrorism expert Pantucci, referring to Islamist extremism. Catalan officials consequently sought to employ counterterrorism officials capable of speaking the various accents common in different parts of the region’s Muslim communities. Acknowledging the need for cross-country-information sharing that still remains flawed in other parts of Europe, Catalan police officials also launched coordinated raids and operations with their Belgian or Moroccan counterparts.

And whereas authorities in Britain or Germany have faced criticism for failing to arrest suspects who showed signs of radicalization early on, Spain has chosen the opposite path. Tougher laws, introduced over the last 12 years and reinforced since 2010, have made it especially easy for authorities to arrest suspects. “If someone watches terrorism videos online, he or she will likely be monitored as a result,” said Carvalho. There has been a spike in Islamist terrorism-related arrests in the country since 2013, likely due to the emergence of the Islamic State and law changes.

The country now has some of Europe’s highest Islamist-terrorism-related arrest ratios, despite a lower number of radicalized individuals in the country overall, compared to Britain or Germany. The two nations have been more cautious to arrest suspects as a preventive measure, citing intelligence-gathering opportunities and human rights concerns. Some countries also fear that a harsh crackdown on Islamists could further alienate the Muslim communities that authorities rely on to receive information about radicalized individuals.

Until Thursday, Catalonian authorities could argue that more frequent arrests might be controversial but at least appear to work.

“But this anticipatory counterterrorism model was not without its limitations, which became apparent over time and finally with the Aug. 17 attacks in Barcelona and Cambrils,” said Madrid-based counterterrorism expert Reinares.

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