CRS INSIGHT
European Security, Islamist Terrorism, and Returning
Fighters
September 15, 2015 (IN10209)
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Kristin Archick, Specialist in European Affairs (karchick@crs.loc.gov, 7-2668)
Paul Belkin, Analyst in European Affairs (pbelkin@crs.loc.gov, 7-0220)
Terrorist Attacks in Europe and Mounting Security Concerns
European concerns about Islamist terrorism have been heightened considerably by several attacks over the last year and
the growing number of European citizens training and fighting with extremist groups in foreign conflicts (especially in
Syria and Iraq). Most recently, on August 21, a Moroccan man—who may have traveled to Syria—was arrested in
France after attempting an alleged terrorist attack on a train traveling from Amsterdam to Paris (six passengers,
including three Americans, stopped the attack). In late June, a man was beheaded during an attempt to blow up a U.S.-
owned chemical factory near Lyon, France; the suspect is a French citizen of Muslim background. Other incidents
include the following:
The May 2014 killing of four people at the Jewish Museum in Brussels, Belgium; a French Muslim who
reportedly spent a year with Islamist fighters in Syria has been charged.
The January 2015 attacks in Paris in which gunmen killed 17 people in three related incidents that targeted the
satirical magazine Charlie Hebdo, police officers, and a kosher supermarket. The perpetrators of the attacks were
French-born Muslims, with possible ties to Al Qaeda in Yemen or the Islamic State terrorist organization.
The February 2015 shootings in Copenhagen, Denmark, in which a Danish-born citizen of Palestinian descent
murdered two individuals—one at a cafe that had been hosting a free speech debate, another at a synagogue—and
wounded five police officers.
Security services warn not only about the potential dangers posed by those who may have trained and fought abroad, but
also about individuals like the Danish gunman or the Lyon suspect who appear to have been inspired by Islamist
extremist propaganda to commit "lone wolf" attacks at home without ever traveling abroad.
Although it is difficult to assess the precise number of Muslims from Europe who have joined extremist groups in Syria
and Iraq, European officials believe that their ranks have increased significantly over the past two years. Estimates from
Europol, the European Union's (EU's) joint criminal intelligence body, suggest that at least 3,000 and upward of 5,000
EU citizens have left to fight in Syria, Iraq, or other conflict zones. A January 2015 study indicates that up to 4,000
individuals from Western Europe have become foreign fighters. Key countries of origin reportedly include Belgium,
Denmark, France, Germany, the Netherlands, Spain, Sweden, and the United Kingdom. The conflict in Syria and Iraq
has also attracted fighters from the Western Balkans (especially Bosnia, Kosovo, and Albania) and Russia. (For more
information, see CRS Report R44003, European Fighters in Syria and Iraq: Assessments, Responses, and Issues for the
United States).
European Policy Responses
European governments have employed a range of measures to combat the foreign fighter threat, including increasing

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surveillance, prohibiting travel, detaining returning fighters, and bolstering counterterrorism laws. Individuals
suspected of having traveled to fight in Syria or Iraq, planning such travel, or recruiting others have been arrested in
Belgium, France, Germany, the Netherlands, Spain, and the United Kingdom (among other countries). Several
European governments have enacted or are considering new legislation to ensure that their laws permit prosecuting
those who travel or attempt to travel abroad for terrorist purposes, as required by U.N. Security Council Resolution
2178 of September 2014. European officials are also seeking to more aggressively counter radicalization and extremist
propaganda, especially via the Internet and social media. Some have called on U.S. technology companies to assist
these efforts by preemptively removing terrorist content from their sites.
France, which is home to Europe's largest Muslim population (about 5-6 million) and the source of the largest number
of European fighters in Syria and Iraq (about 1,400), has been at the forefront of European efforts to counter the threat
posed by Islamist militants. Over the past year, the government has taken steps to strengthen counterterrorism policies
already considered some of the most stringent in Europe. These have included imposing travel bans on individuals
suspected of seeking terrorist training abroad, blocking websites and prohibiting speech that encourage terrorism, and
significantly enhancing the state's surveillance authorities.
Nevertheless, stemming the flow of European fighters to Syria and Iraq and keeping track of those who go and return
remains challenging. Prosecuting individuals preemptively is difficult in because most existing laws require a high level
of proof that a suspect has actually engaged in terrorism abroad or has returned to commit a terrorist act. Furthermore,
even governments with far-reaching legal authorities have been challenged to monitor a growing number of potential
assailants amid budgetary and personnel resource constraints. The suspects in the Brussels, Paris, and Lyon attacks had
all been previously questioned by French authorities, but surveillance was lifted in each case.
Analysts assert that more must be done at the EU level to better combat the foreign fighter threat given the Schengen
system of largely open internal borders (which permit individuals to travel without passport checks among most
European countries). The thwarted train attacker and the alleged Brussels gunman had each reportedly traveled between
several European countries prior to the attacks. The EU has been seeking to enhance information-sharing among
national and EU authorities, strengthen external border controls, and improve existing counter-radicalization efforts,
particularly online. However, implementation of some of these initiatives and other possible measures—such as
harmonizing criminal laws against "jihadi travel" among the EU's 28 member states—has been slowed by national
sovereignty concerns, law enforcement barriers to sharing sensitive information, and civil liberty protections.
Pressure has also increased to approve an EU-wide system for the collection of airline Passenger Name Record (PNR)
data, which stalled in the European Parliament—a key EU institution—in 2013 because of data privacy and protection
concerns. In July 2015, the Parliament's civil liberties committee endorsed a revised PNR proposal, but it must still be
approved by the full Parliament and the EU member states. Critics contend that the envisioned EU PNR system
infringes too much on data privacy rights and does not go far enough in ensuring that PNR data is meaningfully shared
among member states. In the wake of the aborted train attack, the EU is also expected to consider ways to strengthen
rail security.
U.S. Interests
U.S. officials, including some Members of Congress, worry that Europeans fighting with Islamist extremist groups
abroad could enter the United States under the U.S. Visa Waiver Program (VWP), which allows short-term, visa-free
travel for citizens of most European countries (see CRS Report RL32221, Visa Waiver Program). In the 114th
Congress, H.R. 158 and S. 542 largely aim to strengthen the VWP's security components to better guard against
terrorist threats. U.S. policymakers assert that the foreign fighter phenomenon underscores the importance of
maintaining close U.S.-EU counterterrorism cooperation (see CRS Report RS22030, U.S.-EU Cooperation Against
Terrorism); they have also encouraged the EU to establish its own PNR system and to make greater use of existing EU-
wide information-sharing tools.

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