Abstract: Even though there were half as many attacks by Islamic State terrorists in Europe in 2018 compared to 2017, the threat remains high. In 2018, Europe saw more jihadi attack plots than any given year before 2015, and several foiled plots last year could have caused mass casualties. The Islamic State became such a potent threat in Europe partly because of special circumstances surrounding the war in Syria and rise of the Islamic State, and partly because the Islamic State built upon networks already established by al-Qa`ida. Because Europe’s jihadi networks have grown considerably since the outbreak of the Syrian war and strengthened their ties to the global jihad movement through foreign fighting, it is possible there will be future big waves of attacks. There are three main determinants of the emergence of future jihadi cells in Europe in increasing order of importance: military interventions in Muslim countries, jihadi networks, and terrorist entrepreneurs.
On December 11, 2018, just as Europeans were beginning to think the jihadi threat in the region was shrinking, a terror attack struck the Strasbourg Christmas market. A French-Algerian Islamic State supporter, Cherif Chekatt, killed five and injured 12 in an attack with a revolver and knives. After a major manhunt, Chekatt was killed in an exchange of fire with police officers two days later. Investigations turned up a video in which the attacker pledged fealty to the Islamic State, and Chekatt was already known to the security services for having extremist leanings.1 The Strasbourg attack was in tune with how Islamic State-affiliated jihadis have operated in Europea in recent years and a reminder that although the Islamic State is weakened, Europeans are not in the clear from jihadi terror. On the contrary, although there were approximately half as many attacks by Islamic State terrorists in Europe in 2018 compared to 2017,b there is a high potential for future waves of attacks as Europe’s jihadi networks have grown and strengthened their ties to the global jihadi movement since the outbreak of the war in Syria.
What is the actual scope of the Islamic State threat in Europe, and how did we get here? Based upon the author’s previous works on jihadi terrorism in Europe, this article examines what has shaped this threat in the past, and may continue to do so in the future.c The author argues the threat from the Islamic State became so big in Europe because the Syrian war breathed new life into European jihadism and because the Islamic State took over al-Qa`ida’s networks in Europe, making them effective tools for its violent campaign. This article further argues that the variation in the threat to different European countries can be traced to three main factors: 1) military interventions in Muslim countries; 2) jihadi networks; and 3) terrorist entrepreneurs. The author will come back to what each factor entails, but first how much of a threat does the Islamic State pose in Europe?
How Big is the Islamic State Threat to Europe?
Europe has lived with jihadi terror since the mid-1990s when the al-Qa`ida-affiliated Algerian Armed Islamic Group (GIA) carried out a series of bombings in France. In the 2000s, the threat matrix was dominated by al-Qa`ida. Europe saw large-scale attacks such as the train bombings in Madrid in 2004 and the bombings in London in 2005. Al-Qa`ida also plotted a number of large attacks that were foiled in the 2000s. The al-Qa`ida threat continued into the 2010s, before the Islamic State emerged as an international terrorist threat in 2014.
From 2014 onward, nearly all plots in Europe have been linked to the Islamic State, whereas very few have been traced to al-Qa`ida. The level of plotting has reached new heights.2 Never before have there been so many jihadi terrorist plots in Europe as in the period between 2014 and 2018. Never before have so many plots gone undetected and resulted in attacks. Never before have so many Europeans been killed in jihadi terrorist attacks. More people have died from jihadi terrorism in Europe between 2014 and 2018 (at least 345) than in the previous 20 years (at least 267).d
As noted above, in 2018 the number of attacks dropped some 50 percent compared to 2017, and there were no mass-casualty attacks killing more than 10 people. This led many to think that the worst was over and that the military defeat of the Islamic State had decimated the group’s capacity to project terror attacks onto Europe. This view was reflected in a U.N. report in the summer of 2018, which identified a possible causal connection between the drop in attacks and the damaging of the Islamic State’s command and control, especially the death of the group’s most active planners of terror plots.3
It must be stressed, however, that this drop in attack activity followed the unprecedented numbers of attacks seen in 2016 and 2017, and that executed attacks only represent part of the picture. It is a common mistake to gauge terrorist threats by the number of launched attacks only and to not include the plots that were foiled by counterterrorism agencies. When both executed and foiled attacks are looked at, there were actually more jihadi plots in Europe in 2018 than in any given year before 2015. (See Figure 1.e)
The plots in 2018 (both attacks and foiled attacks) demonstrate that the Islamic State remains the main protagonist of jihadi terrorism in Europe. Perpetrators were either inspired by the group or linked to Islamic State networks in Europe, internationally, or online. The plots also show that the Islamic State threat is not merely one of small attacks, but also includes plans for large-scale ones.
In 2018, there were three attacks by single gunmen including Chekatt’s attack in Strasbourg. In March 2018, for example, a Moroccan Islamic State supporter shot policemen and took hostages inside a shopping mall in southern France.4 He killed five, injured 16, and said he was doing it for Syria.5 The year 2018 saw multiple smaller attacks with knives. In May, for example, a French-Chechen Islamic State supporter stabbed a man to death and injured others near the Opéra national de Paris.6 There were also plots in 2018 to use vehicles as weapons; some had the potential to kill dozens as in Nice in 2016. In February, for example, British police arrested a convert who supported the Islamic State and had planned to ram a vehicle into crowds, probably in Oxford Street. He was in contact with Islamic State members in the Philippines.7
The security services also detected plots to employ a toxin in a terror attack. In June 2018, a Tunisian linked to the Islamic State was apprehended in Cologne for allegedly producing ricin to be used in a possible attack.8 He had been in contact with individuals linked to the Islamic State and suspected to be based in North Africa or Syria.9 There was also at least one plan by the Islamic State’s networks in Europe to carry out complex armed assaults like those in Paris in November 2015. In September 2018, for example, seven alleged Islamic State supporters were arrested in the Netherlands for allegedly plotting to attack a public event with assault rifles and hand grenades. The investigation also indicated that they planned to set off a car bomb at another location.10 So even though the number of attacks decreased in Europe in 2018, there was higher plot activity by jihadis in Europe last year than any given year before 2015, and several foiled plots were potentially very lethal. How did Europe get here?
How Did the Threat Get So Big?
In seeking to explain how the Islamic State threat became so big in Europe, it is necessary to distinguish between immediate reasons linked to Syria and the Islamic State, and more general drivers that have shaped the jihadi threat in Europe since the phenomenon emerged in the 1990s. The immediate reasons include the massive mobilization of European foreign fighters, some new tactical moves by the Islamic State, and the refugee crisis.
The civil war in Syria and the rise of the Islamic State breathed new life into European jihadi networks and became major recruitment tools for them. Many European Muslims became enraged by the Assad regime’s abuses of the civilian population. The rise of what to some seemed to be a powerful Sunni ‘state’ implementing sharia and standing up to Assad became a major pull factor for foreign fighting. Over a very short span of time, the recruitment of foreign fighters gave European security services more potential jihadi terror threats to monitor than they had ever dealt with before. A large number of Europeans (estimates vary between 4,000 and 7,000) traveled to Syria as foreign fighters, most of them eventually joining the Islamic State.11
Before the Islamic State’s rise to notoriety and the realization that the group would pose a threat to Europe, it was easy for young European Muslims to travel to Syria via Turkey. Moreover, European states had no clear position vis-a-vis their exodus. Assad’s atrocities in Syria made it hard to condemn those who traveled on moral grounds, and in several countries, legislation was not in place or adapted to ban people from going to Syria.f The early travelers had many and often altruistic motives for going,12 but as soon as jihadis started to dominate the insurgency, most of the Europeans ended up in groups such as Jabhat al-Nusra and the Islamic State.
Historical data shows that a minority (some 11 percent) of foreign fighters who have traveled from Western countries to join conflicts in the Muslim world (for example, Bosnia in the 1990s, or Afghanistan, Iraq, Somalia, and Yemen in the 2000s) ended up becoming international terrorists.13 Yet those who did become such terrorists contributed to making the threat higher. Many of them played roles as terrorist entrepreneurs: recruiting, organizing, training, and directing attack cells. The author will come back to this dynamic later in this article. Islamic State-linked foreign fighters have had a hand in many, if not most of the high-profile attacks and plots in Europe since 2014, either by participating themselves as in the attacks on the Bataclan and other targets in Paris in November 2015, or by directing plotters via an encrypted messaging app, as in the truck attack by Rakhmat Akilov in Stockholm in April 2017.14 g The strength and nature of links between plotters and Islamic State networks have varied significantly it seems, but as the author will return to, plots absent network contacts are very rare in European jihadism.15 h
The second immediate reason for the many plots and attacks attributed to the Islamic State is that the terrorists linked to the group modified their tactics to avoid detection. In 2014-2017, jihadi plots in Europe involved higher proportions of attacks with simple weapons such as cars and knives compared to bombs (which has historically been the preferred weapon of jihadis in Europe), and nearly half of the terrorist plots involved single actors, rather than a group.i Single actors with simple weapons are notoriously difficult to stop. Adding to this, the terrorists increasingly communicated via encrypted apps, which are challenging for security services to monitor. As a result, more plots than ever before went under the radar and resulted in attacks after Islamic State launched its campaign in Europe from 2014.
Lastly, the Islamic State exploited the circumstances of the refugee crisis in 2015 to smuggle operatives among migrants. The most often cited example of this tactic is the Abaaoud network behind the attacks in Paris in November 2015 and in Brussels in March 2016.16 However, there have been multiple other cases in which the Islamic State either sent plotters to Europe posing as refugees or recruited among refugees for attack cells.j The monitoring of growing numbers of foreign fighters and terrorists operating in ways increasingly difficult to detect stretched the capacities of European security services to the limit. So, on one level the threat from the Islamic State became so high in Europe because of a swift increase in the capacities of the terrorists that was not immediately matched by European states. But how did the Islamic State gain such capacities, and what drove its campaign of terrorism in Europe?
Many debates about the drivers of Islamic State terrorism in Europe have revolved around immigration and failed integration. There are certainly links between the immigration of some individuals and jihadism in Europe. Many of those who established jihadi networks in the region in the early 1990s were, for instance, political refugees. And, as noted, refugees (fake or real) have been implicated in plots.
However, at the same time such factors reveal little about when and where the Islamic State strikes in Europe. If levels of immigration from Muslim-majority countries were the main predictor, there would have been more attack activity in countries such as Italy and Sweden, which face high levels of such immigration (but relatively few attack plots).k And if, for example, integration policy was a main predictor, one might see different threat levels in countries with opposing integration policies, such as Britain and France. Britain practices multi-culturalism whereas France practices assimilation, and yet the countries face similar threat levels—the highest in Europe. The main reasons why these two countries face such high threats have to do with 1) their policies of intervening in armed conflicts in the Muslim world; 2) the dynamics of their domestic jihadis networks, including the presence of extremist clusters linked to radical preachers; and 3) the presence in these countries of terrorist entrepreneurs, who build international attack cells on behalf of groups such as al-Qa`ida and the Islamic State.
Revenge for Military Interventions Matter
One main reason that the Islamic State threat became so big in Europe is that the group set out to strike back at European countries that joined the coalition against them.
Historically, jihadis have justified attacks in Europe with reference to two main grievances: military interventions in Muslim countries and perceived insults against Islam (such as drawings of the Prophet Muhammad). The interventions seem, however, to be the main trigger. Statistics on jihadi attack plots in Europe since the 1990s (see Figure 1) show that numbers have increased with Western interventions in Muslim conflicts.
The first increase occurred in the mid-1990s when Algerian Islamists accused France of supporting the military regime during the civil war in Algeria. The al-Qa`ida-linked Algerian terrorist group GIA declared war on France and executed a string of attacks in the country. The next increase came in the mid-2000s following the U.S.- and U.K.-led invasion of Iraq in 2003. Jihadis targeted European countries that were part of the coalition that went into Iraq and major attacks occurred, such as the bombings of commuter trains by an al-Qa`ida-linked terrorist cell in Spain in 2004 and the al-Qa`ida-directed 2005 London bombings. Multiple attack plots were also thwarted in this period, such as an ambitious plan to bring down transatlantic passenger jets departing from the United Kingdom in 2006. The third increase came with the establishment of the Islamic State and the launch of the anti-Islamic State coalition in September 2014. Islamic State-leaders pledged to punish countries attacking the group, and Islamic State terrorists shouted “this is for Syria” when they struck in Europe.l
The geographical distribution of terrorist plots in Europe further shows that those countries with the heaviest military involvement in the Muslim world—France and the United Kingdom—are most targeted.17 Conversely, countries with less military involvement such as Italy or Sweden are less targeted. Another sign that military interventions matter is that many plots target military personnel and installations. Both al-Qa`ida and Islamic State-linked or-inspired terrorists have gone after military targets. The shooting of soldiers in southern France by the al-Qa`ida-linked French-Algerian Mohammed Merah in 2012 is one example. The murder of Fusilier Lee Rigby in Woolwich in 2013 is another. In 2014, a U.K. medical student Tarik Hassane and fellow student Suhaid Majeed made plans for an attack on the Parachute Regiment Territorial Army Barracks at White City in London. Hassane and Majeed were reportedly instructed by the Islamic State via social media.18
Some have asserted that European military interventions did not influence the Islamic State threat to Europe all that much, pointing to the fact that the organization’s forerunner—the Islamic State in Iraq and Syria (ISIL)—was plotting against European countries well before the anti-Islamic State coalition was announced.19 While plots linked to ISIL started appearing in Europe from at least February 2014 when a returned French foreign fighter, Ibrahim Boudina, was arrested in Nice with explosives and a handgun and believed to be preparing an attack on the Nice carnival,20 the rate of plotting increased dramatically after the anti-Islamic State coalition was formed and Islamic State spokesman al-Adnani in September 2014 called for attacks in Europe.21 In addition, it should come as no surprise that there was plotting before 2014. Many among the Europeans who joined the Islamic State as foreign fighters were already part of networks supporting al-Qa`ida that never stopped plotting attacks in Europe. The aforementioned Ibrahim Boudina was part of the Cannes-Torcy network, which recruited for al-Qa`ida-affiliated Jabhat al-Nusra before members joined ISIL. A central member of the network, Jeremie Louis-Sidney, was suspected to have carried out an attack with a hand grenade on a Jewish grocery store in a Paris suburb in 2012 and was later killed by police.22 There are, however, many cases illustrating how the distinction between the Islamic State and al-Qa`ida has not been perfectly clear-cut among jihadis in Europe. In the attacks on Charlie Hebdo and a Jewish supermarket in Paris in January 2015, for example, two jihadis linked to al-Qa`ida in Yemen and an Islamic State supporter cooperated. They had all been part of the same network of al-Qa`ida supporters within France that sent foreign fighters to Iraq and Yemen in the 2000s.23 Both al-Qa`ida and the Islamic State consider attacks in Europe legitimate and wish for them to happen, and as the author will come back to in the next section, their European networks have overlapped.
Jihadi Networks Matter More
While most Islamic State plots have occurred in France and the United Kingdom—the countries that have been most heavily involved in the fight against the group—countries with lighter or less visible contributions have also been targeted.24 Germany, for example, has faced a high threat, although its contribution to the anti-Islamic State-coalition has been relatively limited compared to France and Britain.25 The reason Germany has seen significant jihadi attack plotting is arguably because of the strength and evolution of extremist networks in the country.
Historically, jihadis have sought to launch attacks in European countries they see as legitimate targets, provided they have the capability to operate in those countries. The capability to operate, in turn, relies strongly on links and interaction between groups in conflict zones (al-Qa`ida or the Islamic State) and local networks in Europe. As such, opportunistic attacks may occur in countries that are not at the very top of the jihadis’ list of enemies, but where network links make attacks more likely to succeed. Such links usually come into existence when European Islamist extremists seek out armed groups in conflict zones as foreign fighters. The foreign fighters then become the bridgehead through which groups in conflict zones may gain access to extremist networks within Europe and exploit them either as logistical support networks or for attacks.
After al-Qa`ida embarked on global jihad in 1998, for example, the jihadi networks in Europe became an important weapon against the United States’ European allies. Multiple European jihadis who traveled to conflict zones as foreign fighters were recruited by al-Qa`ida for attacks at home. The threat to the United Kingdom increased in the mid-2000s when al-Qa`ida in the Afghanistan-Pakistan border region recruited British-Pakistani foreign fighters as terrorists. Another example is that the threat to Germany increased in 2007 after a network composed of German converts and German Turks in Neu-Ulm connected with the al-Qa`ida-linked Uzbek Islamic Jihad Union (IJU) in Waziristan, Pakistan. The network was recruited by a Pakistani who operated as an agent for al-Qa`ida-affiliated groups in Germany and members trained with IJU before returning to plot attacks.26
This pattern repeated itself with the Islamic State. A crucial reason why Britain, France, Belgium, and Germany have experienced so many Islamic State-plots is that these countries have had substantial jihadi networks since the 1990s, which produced many foreign fighters for Syria. The main recruitment platform for the Islamic State in Europe was a network that grew out of the U.K.-based al-Muhajiroun movement that initially supported al-Qa`ida and mobilized a new generation of European jihadis during the 2000s.27 After being banned in the United Kingdom, this movement reappeared under the name Islam4UK and under the leadership of the British-Pakistani lawyer and radical preacher Anjem Choudary. It then branched out transnationally across Europe, establishing Sharia4Belgium, Sharia4Holland, Sharia4Spain, Sharia4Denmark (Kaldet til Islam), Sharia4Finland, Sharia4Italy, Sharia4France (Forsane Alizza), Millatu Ibrahim (Germany), and The Prophet’s Umma (Norway).28 In addition to the transnational Sharia4, which staged public events and demonstrations in support of jihadism, European foreign fighters were also dispatched by different local jihadi networks that were more secretive in their support for global jihad. One such network was that of Khalid Zerkani in Brussels, which recruited Abdelhamid Abaaoud, the ringleader of the Paris attacks of November 2015.29 Another example is the Abu Walaa network in Germany to which the attacker of the Berlin Christmas market in 2016 was linked.30
A significant number of Europeans who joined the Islamic State via Sharia4 or networks such as Zerkani’s became implicated in the group’s program for international operations, and ended up as entrepreneurs of attack cells in their home countries.31
Terrorist Entrepreneurs Matter Most
There is a reoccurring pattern in how jihadi terror cells form in Europe, in that a core cadre of experienced jihadis with links to groups in conflict zones, such as al-Qa`ida and the Islamic State, recruit attackers locally on European soil. These terrorist entrepreneurs are activists who dedicate themselves to furthering the aims of the groups they represent.
The entrepreneurs reach out to misfits (criminals and social losers) and offer them purpose and community, or recruit drifters from their own social networks, and mold them into terrorists.32 The process is truly transnational in that entrepreneurs operate across borders within Europe and interact with jihadis in Muslim countries. The entrepreneurs also represent historical continuity in European jihadism because of the way that many of them have turned up in different terror investigations over time. In several cases, people who acted as entrepreneurs in Europe during the 2000s and even the 1990s have reappeared in plots by Islamic State since 2014.
Oftentimes, the entrepreneurs have built attack cells in a very hands-on fashion, in the context of radical mosques and underground networks in Europe. At other times, they have coordinated cells from conflict zones, using middlemen or social media. Then there are examples of entrepreneurs who have operated within jails and influenced people who later participated in terror attacks. A new development with the Islamic State is that “virtual entrepreneurs” have recruited and directed terrorists for attacks in Europe and elsewhere in the West solely via encrypted apps such as Telegram.33
A famous example of a terrorist entrepreneur who has reappeared is the French Algerian Djamel Beghal who recruited for the GIA in Europe in the 1990s, built terror cells for al-Qa`ida around the millennium (for which he was arrested in 2001), and then influenced the perpetrators of the attacks on Charlie Hebdo and a kosher supermarket in January 2015. He interacted with some of them while he was in jail and all of them when he was out on parole in 2010.34 Another example of historical continuities and the role of jails is the entrepreneur of the terrorist cell, linked to or inspired by the Islamic State, behind the attacks in Barcelona in August 2017. Abdelbaki Es Satty reportedly came under the “malign influence” of a central member of the terrorist cell that launched the attacks in Madrid in 2004 and other extremists while in prison.35 A third possible example on how veteran terrorist entrepreneurs re-emerge in the backdrop of new plots was revealed in 2017. It was reported that another imprisoned GIA veteran, Lionel Dumont, was linked to Islamic State supporters arrested in 2017 in Wattignies in northern France was suspected of recruiting and plotting an attack for the group in France or Belgium. Before his arrest in 2003, Dumont had as a terrorist entrepreneur directed the activities of the Roubaix Gang, which robbed banks and plotted attacks in support of the GIA in the mid-1990s, and had then spent time in Southeast Asia, where according to some investigators he may have worked on behalf of al-Qa`ida. One of the purported plotters arrested in Wattignies had spent time in prison with Dumont and was alleged to have been influenced by him. Both of them had communicated with the veteran in jail, and a search of Dumont’s cell turned up Islamic State propaganda. Dumont denied any involvement in a terror plan and said the pair had provided him with the propaganda.36
A hands-on entrepreneur from the Islamic State era is Abdelhamid Abaaoud who directed the cell behind the deadly attacks in Paris in November 2015. Abaaoud had also directed an Islamic State terror cell in Verviers, which was planning attacks, possibly on police stations, a plot that was thwarted after a shootout with Belgian counterterrorism commandos in January 2015. Abaaoud escaped the dragnet of the security services and went back to the Islamic State in Syria, only to return to coordinate the biggest attack in Europe since the Madrid bombings.37
What caught European security services off guard and contributed strongly to the high frequency of plots and attacks by Islamic State in Europe was the ability of European foreign fighters in Syria and Iraq to act as entrepreneurs from conflict zones via encrypted apps. Examples include, among others, the French foreign fighter Rachid Kassim38 who directed multiple plotters in France, such as Larossi Abdalla who killed a policeman and his wife in Magnanville in 2016,39 and British foreign fighter Junaid Hussein who guided cells in the United Kingdom, the United States, and Australia.40
Despite the fact that the number of attacks has decreased, it is way too early for Europe to lower its guard against jihadism. It must be expected that Islamic State followers will continue to seek to punish Europeans for their contribution to bringing down the ‘caliphate.’ Also, it cannot be ruled out that European governments in the future will again intervene militarily in Muslim countries.
Furthermore, if history repeats itself, the unprecedented number of Europeans who departed for Syria will lay the groundwork for future jihadi networks that will target Europe. The foreign fighting has undoubtedly strengthened transnational ties between jihadis within Europe as well as their ties to groups in multiple conflict zones. If jihadis find new safe havens in war-torn countries such as Iraq, Syria, Libya, and Afghanistan, or in the Sahel region in the time ahead, such ties could be exploited as bridgeheads by groups that want to take the fight to Europe.m And among the large number of European foreign fighters, there is almost certainly a substantial number of individuals who could emerge as tomorrow’s entrepreneurs of terror cells.
Adding to this, the broader jihadi mobilization caused by the civil war in Syria has undoubtedly increased the pool of Islamist extremists in Europe. A recent report set the number of Islamist extremists in Germany at 25,000. The report stated that 2,240 of them had the potential of becoming jihadi terrorists.41 The United Kingdom is home to up to 25,000 Islamist extremists, of whom about 3,000 are seen as a threat and about 500 are under constant surveillance.42 In France, some 20,000 were included in the FSPRT watchlist as radicalized in February 2018. The list contains a broad spectrum ranging from men who reject shaking the hands of women to potential terrorists, and is constantly updated. Some 4,000 are seen as a potential terrorist threat and monitored closely.43 European prisons have also been filling up with jihadis. Of the 1,500 foreign fighters who have returned, several hundred have been imprisoned.44 Some of them will likely leave extremism behind, but others will re-join an extremist scene that has grown in recent years. Moreover, jihadis who have been imprisoned during the 2000s are being released. It was estimated, for example, that 80 of the 193 individuals convicted of terrorism crimes in the United Kingdom since 2007 (about 40 percent) were scheduled to be released by the end of 2018.45
Since the Islamic State threat escalated, European governments have allocated resources to counterterrorism, and Europe’s stance on terrorism has toughened considerably. There is more surveillance; more people are arrested for extremist activities; and some countries, such as France, have pursued a policy of killing their own citizens in Islamic State-held areas because they are seen as a threat.46 The tougher measures have surely stopped attacks, but the terrorists keep plotting, and can frame the harder measures as a ‘War on Islam’ to mobilize new recruits.
The most recent wave of jihadi terrorism in Europe appears to have crested, but European security agencies should prepare themselves for a future wave that may already be forming. CTC
Petter Nesser is a senior researcher at FFI’s Terrorism Research Group and the author of Islamist Terrorism in Europe (London: Hurst/OUP, 2015; 2nd edition, 2018). Follow @petternessern
[a] Europe is here defined as Western Europe, not including former Eastern Bloc states.
[b] According to FFI’s dataset on jihadi attack plots in Western Europe maintained by the author and Anne Stenersen (last updated December 2018), there were 16 attacks in 2017 and seven in 2018. FFI registered six attacks in 2015 and 11 in 2016.
[c] The analysis presented here draws from and expands on the epilogue to the second edition of the author’s book Islamist Terrorism in Europe (London: Hurst/OUP, 2018) and his article “Europe hasn’t won the war on terror,” Politico, December 5, 2018.
[d] Numbers of deaths taken from FFI’s dataset on jihadi attack plots in Western Europe.
[e] The graph is based on FFI’s dataset on jihadi attack plots in Western Europe.
[f] E.U. efforts to adapt laws to stem the foreign fighter flow to Syria gained traction with the rise of the Islamic State in 2014 and intensified with the attacks on the Bataclan and other targets in Paris in 2015. See, for example, “The challenge of foreign fighters and the EU’s response,” Council of the European Union, October 9, 2014, and “The return of foreign fighters to EU soil,” European Parliament, May 2018.
[g] In “Jihadi Terrorism in Europe: The IS-Effect,” Perspectives on Terrorism 10:6 (2016), the author and his co-authors (Anne Stenersen and Emilie Oftedal) did a preliminary analysis of 38 Islamic State-linked plots and attacks in Europe between 2014 and October 2016, and they found that 19 plots were reported to have involved contacts with and guidance from members of Islamic State networks via social media. See p. 8. Of the 38 plots, the study further found 12 cases that could be linked to Islamic State’s section for international operations with a high degree of certainty.
[h] The idea that terrorists can operate in complete isolation as ‘lone wolves’ has increasingly come under critique. For a recent contribution to debunking the lone-wolf myth, see Bart Schuurman, Francis O’Connor, Lasse Lindekilde, Noemie Bouhana, Paul Gill, and Stefan Malthaner, “End of the Lone Wolf: The Typology That Should Not Have Been,” Studies in Conflict & Terrorism (2017): pp. 1-8.
[i] For example, in the period 2008-2013, 65 percent of plots involved some kind of bomb dimension, whereas in 2014-2016, the proportion fell to 33 percent. Only 13 percent of plots in 2008-2013 involved knives, whereas the proportion increased to 33 percent in 2014-2016. For more on changes in weapons and tactics, see Petter Nesser, Anne Stenersen, and Emilie Oftedal, “Jihadi Terrorism in Europe: The IS-Effect,” Perspectives on Terrorism 10:6 (2016), p. 11-13. See also Nesser and Stenersen, “The Modus Operandi of Jihadi Terrorists in Europe,” Perspectives on Terrorism 8:6 (2014) for more on the historical trends in the modus operandi of jihadis in Western Europe.
[j] For example, Anis Amri was a failed asylum seeker to Italy and Germany. He mixed with an Islamic State recruitment network in Germany and communicated with Islamic State handlers abroad both before and during the attack on the Berlin Christmas market. See, for example, “Berlin Christmas Market Attacker Got Order Directly from Islamic State,” Reuters, April 15, 2017.
[k] FFI’s database on jihadi attack plots in Western Europe distinguishes between well-documented and vague plots, according to the extent to which plots fulfill the following criteria: 1) identified jihadi actor; 2) identified target(s); and 3) evidence of attack plan (e.g., confiscated weapons and scouting of targets). In 2014-2017, FFI registered no well-documented plots in Italy and four in Sweden.
[l] For example, the November 2015 Paris attacker cell. See Kim Willsher, “Attack at Paris’s Bataclan: ‘two or Three Men Began Shooting Blindly at Crowd,” Guardian, November 14, 2015. Or the Islamic State supporter who attacked police outside Notre Dame. See “Paris: French Police Shoot Attacker Armed with Hammer at Notre-Dame Cathedral,” Local, June 6, 2017.
[m] According to the United Nations, there have already been foiled plots in Europe linked to Islamic State militants in Afghanistan. “Twenty-second report of the Analytical Support and Sanctions Monitoring Team,” United Nations, July 27, 2018, p. 16.
 Alissa J. Rubin, Aurelien Breeden, and Elian Peltier, “Strasbourg Shooting Suspect, Chérif Chekatt, Is Killed by French Police,” New York Times, December 13, 2018; Kim Willsher, “Chérif Chekatt: Who Is the Strasbourg Shooting Suspect?” Guardian, December 12, 2018.
 “Twenty-Second Report of the Analytical Support and Sanctions Monitoring Team Submitted Pursuant to Resolution 2368 (2017) Concerning ISIL (Da’esh), Al-Qaida and Associated Individuals and Entities – United Nations Security Council Counter-Terrorism Committee,” July 27, 2018, p. 6.
 For assessments of the European foreign fighters, consult Richard Barrett, “Beyond the Caliphate: Foreign Fighters and the Threat of Returnees,” Soufan Center, October 2017, or Thomas Renard and Rik Coolsaet, “Assessing Policies on Returning Foreign Terrorist Fighters in Belgium, Germany and the Netherlands,” Egmont Institute, February 2018.
 See, for example, “The Threat to Denmark from Foreign Fighters in Syria,” CTA, December 4, 2013 and Angel Rabasa, Eurojihad: Patterns Of Islamist Radicalization And Terrorism In Europe (New York: Cambridge University Press, 2014), p. 139.
 Thomas Hegghammer, “Should I Stay or Should I Go? Explaining Variation in Western Jihadists’ Choice between Domestic and Foreign Fighting,” American Political Science Review 107:1 (2013): pp. 1-15.
 See Petter Nesser, Islamist Terrorism in Europe (London: Hurst/OUP, 2018), pp. 253-265 and 300-302.
 Richard Spillett and Duncan Gardham, “Tarik Hassane and Suhaib Majeed Jailed for Life for ISIS-Funded Terror Plot,” Mail Online, April 22, 2016.
 Paul Cruickshank, “Raid on ISIS suspect in the French Riviera,” CNN, August 28, 2014; “Jérémie Louis-Sidney, l’apprenti terroriste qui voulait ‘finir en martyr,’” France 24, October 7, 2012.
 See, for example, “‘Buttes Chaumont’ network behind Paris attacks,” Channel 4 News, January 9, 2015.
 See Nesser, Stenersen, and Oftedal, pp. 14-15, and Nesser, Islamist Terrorism in Europe, pp. 53-66.
 See, for example, Guido W. Steinberg, German Jihad: On the Internationalization of Islamist Terrorism (New York: Columbia University Press, 2013), pp. 77-103.
 See, for example, Jackson and Brisard.
 Nesser, Islamist Terrorism in Europe, pp 12-18.
 Nesser, Islamist Terrorism in Europe. See also Scott Sayare’s excellent article, “The Ultimate Terrorist Factory,” Harper’s Magazine, January 2016.
 James Rothwell and Martin Evans, “Imam behind Barcelona Terror Cell Had Links to Madrid Bomber,” Telegraph, August 20, 2017; Fernando Reinares and Carola Garcia-Calvo, “‘Spaniards, You Are Going to Suffer:’ The Inside Story of the August 2017 Attacks in Barcelona and Cambrils,” CTC Sentinel 11:1 (2018).
 See, for example, Jean-Michel Décugis, “Les inquiétantes relations de l’ex-braqueur suspecté d’avoir fomenté un attentat,” Parisien, July 23, 2017; Jacques Laruelle, “L’ombre du “gang de Roubaix” autour des frères Saouti,” DH, July 13, 2017; Christophe Dubois, “Le cerveau du gang de Roubaix arrêté,” Parisien, December 16, 2003; Eric Talmadge, “Al-Qaeda agent lived quiet life in Niigata,” Associated Press, June 2, 2004.
 Report before Deutcher Bundestag, dated November 9, 2018.
 See, for example, “European Union Terrorism Situation and Trend Report 2018.” A recent U.N. report stresses that prison radicalization remains a significant challenge. See “Letter dated 15 January 2019 from the Chair of the Security Council Committee,” United Nations.
 See Thomas Hegghammer, “Europe to Terrorists: It’s No More Monsieur Nice Guy,” Wall Street Journal, October 7, 2018. See also “Wanted dead, not alive: France’s approach to French jihadists,” Local, October 18, 2017.