Three Americans and a British man subdued armed gunman Ayoub El-Khazzani on a high-speed train between Amsterdam and Paris on Aug. 21, another reminder of Europe’s susceptibility to attacks by individual radical Islamists apparently working alone. Here’s why continental Europe is particularly vulnerable to such attacks:
ISLAMIST INFLUENCE
Officials say many of the 5,000 Europeans who have fought with extremist groups like ISIS or al-Qaeda’s Nusra Front in Iraq and Syria return eager to stage attacks; these include Khazzani, who is believed to have traveled to Syria last year. Others are radicalized from afar, like the Paris gunman who killed four people in a kosher supermarket in January.
ACCESS TO GUNS
Though the E.U. has some of the world’s strictest gun-control laws, its proximity to former conflict zones in the Balkans means that aspiring terrorists have access to some 3 million illicit weapons still in circulation there–including Kalashnikovs found when police discovered an arms cache in Belgium in January.
POROUS BORDERS
Freedom of movement within the E.U. means anyone can cross borders by rail or road with few security checks, and there is no pan-European no-fly list. Security services, already struggling to prevent Europeans from joining extremists abroad, have the near impossible task of identifying which individuals are intent on carrying out small-scale attacks that require little planning or coordination. Diplomatic officials say greater intelligence sharing is crucial to curtail the problem.
–NAINA BAJEKAL
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Write to Naina Bajekal at naina.bajekal@time.com