European Security and Islamist Terrorism

The June 3, 2017, attack in London—in which 8 people were killed and nearly 50 injured—was the third terrorist incident in the United Kingdom in the past few months. Five people were killed outside the UK parliament in March in a similar car and knife attack, and in May, a suicide bomber killed 22 people and wounded 116 at a music concert in Manchester. These incidents are among a string of terrorist attacks in Europe connected to or inspired by violent Islamist extremism, with many since 2014 linked to the Islamic State group (also known as ISIS or ISIL). (For more information, see CRS In Focus IF10561, Terrorism in Europe.)

European governments and the European Union (EU) have been alarmed by the rise of the Islamic State in Syria and Iraq and its reach into Europe. EU authorities estimate that up to 5,000 EU citizens have traveled abroad to join the Islamic State and other jihadist groups. U.S. officials view the November 2015 attacks in Paris (which killed 130 people) and the March 2016 bombings in Brussels (in which 32 people died) as indications of the Islamic State's capacity to direct attacks beyond Syria and Iraq. All of the identified Paris and Brussels assailants were European citizens; some fought in Syria and/or Iraq and may have been connected to a "European branch" of the Islamic State.

At the same time, European authorities warn about the dangers of "lone wolf" terrorists motivated by the Islamic State's media-savvy propaganda. Although the Islamic State frequently claims those responsible for such attacks are its "soldiers," evidence suggesting a direct connection varies and is absent in some cases. As in several other attacks—including those in Nice, France, and Berlin, Germany, in 2016, and in Stockholm, Sweden, earlier this year—those responsible for the March and June attacks in London used vehicles as weapons, in line with Islamic State propaganda that encourages followers in Western countries to murder "disbelievers" with any means available.

The Manchester bombing—carried out by a young British citizen of Libyan descent—has exacerbated concerns that the Islamic State could be seeking to direct attacks from Libya given the group's presence and activities there. The Manchester investigation remains underway, but press reports suggest that the attacker was in contact with Islamic State fighters in Libya. Media reports also link the perpetrator of the 2016 Berlin truck attack to the Islamic State in Libya.

European Responses and Challenges

Europe has grappled with domestic and foreign terrorist groups for decades. Especially since 2001, European governments and the EU have devoted increased attention to combating terrorism through stronger law enforcement measures and enhanced antiterrorism legislation.

France and the United Kingdom have been at the forefront of European efforts to counter Islamist militants and the foreign fighter phenomenon. Belgium, Germany, and many other European countries also have sought to increase surveillance, prohibit traveling abroad for terrorist purposes, and more aggressively tackle radicalization and extremist propaganda, especially on the Internet and social media. Following the June attacks in London, UK officials called on Internet and technology companies to do more to remove terrorism content from their sites.

Nevertheless, the recent terrorist attacks have highlighted shortcomings in national domestic security frameworks and EU-level information-sharing and border controls. For many European countries, monitoring a growing number of potential assailants has been challenging amid budgetary and manpower constraints. Despite being known to European security services, some assailants have easily moved around Europe by taking advantage of the Schengen system, which largely permits passport-free travel among most European countries. In other cases, the perpetrators of an attack had been identified by authorities in one EU country as posing a potential threat, but the information was not shared with counterparts in the countries where attacks ultimately occurred.

The EU has made some progress in addressing these security gaps. Measures include adopting EU-wide rules for the collection of airline passenger data and enhancing external border checks. However, improvements have often been slowed by national sovereignty concerns, law enforcement barriers to sharing sensitive information, and data privacy and civil liberty protections.

The uptick in terrorist activity and the fact that many perpetrators were European citizens has reinforced long-standing anxieties about the integration of Muslims in Europe. Several terrorist attacks in Germany in 2016 were carried out by refugees or asylum-seekers, and experts note that such individuals may be particularly vulnerable to violent extremist propaganda due to trauma and dislocation. European governments also have faced pressure to improve counter-radicalization efforts in prisons. At the same time, certain policies targeting Muslims (such as banning some forms of Islamic dress) could increase a sense of alienation and exacerbate the potential for radicalization.

Issues for the United States

Successive U.S. Administrations and many Members of Congress have long been concerned about terrorism in Europe and its implications for U.S. interests. One American was killed in the November 2015 Paris attacks, four in Brussels and three in Nice in 2016, and one at the UK parliament in March 2017. President Trump strongly condemned the latest attacks in Manchester and London, and he asserted that the attacks demonstrated the need for the Administration's proposed "travel ban" on citizens from certain Muslim-majority countries.

The spate of terrorist attacks in Europe may prompt further congressional scrutiny of counterterrorism policies and initiatives to combat violent extremism. The U.S. Visa Waiver Program (VWP), which allows short-term, visa-free travel for citizens of most European countries, has been a key congressional focus. Despite measures enacted in late 2015 to strengthen the security of the VWP, some Members of Congress remain concerned that the program could allow Europeans connected with Islamist militants to enter the United States.

Many Members of Congress support close U.S.-European counterterrorism cooperation and may be concerned that reported U.S. leaks related to the Manchester investigation could damage U.S.-UK intelligence relations. The attacks in Europe could also raise additional questions for Congress about U.S. efforts to counter the Islamic State in Syria, Iraq, and Libya. (For additional information, see CRS Report RL32221, Visa Waiver Program; CRS Report RS22030, U.S.-EU Cooperation Against Terrorism; and CRS Report R43612, The Islamic State and U.S. Policy.)