The United States faces an unprecedented threat from terrorism today: two transregional networks actively plot attacks, recruit foreign fighters, and seek to inspire “lone wolf” terrorists. But this threat is manageable. Rather than trying to defeat terrorist adversaries, U.S. strategy should emphasize reducing the risk of significant attacks in the homeland, Western Europe, Canada, and Australia. In addition to homeland security measures, such a strategy would be characterized by a shift, and likely an increase, in the placement of U.S. special operations forces and intelligence assets overseas. Managing this threat would also require greater coordination with, and persistence from, other instruments of national power, including diplomacy and law enforcement. The key counterterrorism challenge for a new administration, therefore, is how to develop and sustain a strategy that manages this threat persistently, without being on a constant war footing. 

This chapter addresses the counterterrorism challenges facing U.S. policymakers today. To do so, it focuses on foreign terrorist groups and how they threaten the United States and its allies in Western Europe, Canada, and Australia. Of course, most of these terrorist groups also pose a threat to regional stability, as addressed in other chapters. But this chapter prioritizes the safety of the U.S. homeland, citizens, and residents. It argues that not only the primary threat to the United States comes from two transregional terrorist networks but also that the Nation faces an unprecedented threat from foreign fighters and individuals inspired by those transregional networks. This combination can be difficult to disrupt persistently, whether overseas or inside the United States.¹ So the key counterterrorism challenge for policymakers today is how the U.S. Government can manage this threat without being on a constant war footing. 

Threats Posed by Terrorist Networks 

This section provides an overview of the foreign terrorist and insurgent groups that pose a threat to the United States, as well as the nature and extent of that threat. Note that significant research exists on how and why terrorism arises, why individuals become involved in terrorism, how terrorist groups generate and maintain support, and why terrorism declines.² This section does not delve into that research. Instead it posits that groups with transregional objectives and reach present the greatest threat to the U.S. homeland and its allies in Western Europe, Canada, and Australia. Subsequent sections address the threats posed by foreign fighters and lone wolves in greater depth. 

The Islamic State and Its Provinces 

The primary threat to the U.S. homeland today emanates from the Islamic State of Iraq and the Levant (ISIL).³ Led by Abu Bakr al-Baghdadi, ISIL maintains its headquarters in Raqqah, Syria, and Mosul, Iraq. Beyond these two cities, ISIL either controls movement (or at the very least retains freedom of movement) across territory in both countries (see figure 1).⁴ So it is often referred to as a terrorist group, an insurgency, and a proto-state. ISIL has an estimated 20,000 to 30,000 local fighters, as well as foreign fighters, also known as “volunteers,” who have traveled to Iraq and Syria to assist with the struggle against Syrian President Bashar al-Asad and join ISIL’s newly established caliphate.⁵ Experts assess that ISIL had an annual revenue of between $265 million and $615 million as of late 2015, stemming from local taxation, oil, kidnapping for ransom, smuggling, and other forms of crime, although their revenue decreased in 2016.6 ISIL leaders utilize this revenue, and personal relationships built over the years, to reinforce their authority over “provinces” that have been established outside the borders of Syria and Iraq, including Afghanistan, Algeria, Bangladesh, Egypt, Indonesia, Libya, Nigeria, Pakistan, Russia (Chechnya), Saudi Arabia, Somalia, and Yemen.⁷ 

In June 2014, ISIL spokesman Abu Muhammad al-Adnani announced the creation of an Islamic caliphate in the territory under ISIL’s control in Iraq and Syria, changing his organization’s name from the Islamic State of Iraq and the Levant to simply “Islamic State.”⁸ The primary message from al-Adnani at the time was that the Islamic State had established governing structures and religious law in its territories, and thus all Muslims had a religious obligation to transfer their allegiance to ISIL and relocate to this newly established caliphate.⁹ Al-Adnani’s announcement was accompanied by additional military victories, territorial gains, and a concerted social media campaign to terrorize local and international opponents in 2014 and 2015.¹⁰ Militant groups in the outlying provinces of ISIL’s so-called caliphate also have followed its lead, adopting ISIL tactics and using social media to advertise their campaigns. 

While most of this violence has been directed inward or toward the local residents of territories under dispute, ISIL and its affiliates also have attacked international targets. Examples of international terrorist attacks by ISIL and loyal groups include: 

• August 2014: ISIL fighters decapitated American journalist James Foley. The beheading was videotaped and posted online.¹¹ 
• June 2015: A gunman attacked a beach vacation resort in Tunisia, killing 38 individuals.¹² 
• November 2015: Paris came under attack by ISIL fighters; 129 people died.¹³ 
• March 2016: Twin suicide attacks on the airport and subway system in Brussels killed 32 individuals; responsibility for the attacks was claimed by ISIL. 

Notably, prior to the Paris and San Bernardino attacks, terrorism experts debated whether ISIL or al Qaeda presented the greatest threat to the United States, especially the U.S. homeland.¹⁴ This debate centered on two key assumptions. First, some experts assumed that ISIL leaders were focused exclusively on the battle for control over territory in Syria and Iraq and, therefore, would not attempt to reach beyond those countries. As a corollary, because ISIL leaders prioritized the near enemy (for example, so-called apostate Muslim regimes) over the far enemy (for example, the United States), it would not sponsor external attacks.¹⁵ 

Second, other experts assumed that ISIL would experience a backlash among Muslim communities for its brutality on the battlefields of Syria and Iraq. Examples of ISIL brutality included the widely disseminated beheadings of Western journalists.¹⁶ ISIL also captured and then burned alive a Jordanian pilot in February 2015. This assumption drew on past experience with ISIL’s predecessor, al Qaeda in Iraq (AQI), which faced significant backlash after its members conducted its own decapitation campaign against Iraqi officials and foreign journalists throughout 2004 and then subsequently attacked a wedding party in Jordan in November 2005.¹⁷ 

Yet events eventually called both of these assumptions into question. In the early summer of 2014, for example, rumors circulated that ISIL had begun to reach out to militant groups that were associated with al Qaeda but were disgruntled with its leadership and direction. These rumors were substantiated several months later as terrorist groups in Afghanistan, Algeria, Chechnya, Egypt, Libya, Nigeria, Saudi Arabia, Somalia, and Yemen declared their allegiance to, and were formally accepted by, ISIL.¹⁸ 

Additionally, an unprecedented number of foreign fighters—30,000 in Iraq and Syria and 5,000 in Libya by November 2015—continued to travel overseas to join ISIL.¹⁹ This constant flow of foreign fighters, even after the highly publicized beheadings, suggested that the anticipated backlash was unlikely to occur. It was coupled with an escalating number of plots both directed and inspired by ISIL leadership.²⁰ Indeed, investigations into the Paris and Brussels attacks subsequently revealed that al-Adnani had been given responsibility over external operations as early as January 2014.²¹ It therefore became increasingly obvious that ISIL posed the greater threat to North America, Western Europe, and Australia. 

Al Qaeda and Its Affiliates 

If ISIL represents the primary terrorist threat to the United States in 2016, al Qaeda and its associates should not be ignored entirely. Currently led by Ayman al-Zawahiri, al Qaeda was responsible for the attacks on the World Trade Center and the Pentagon in September 2001.²² It has been a prominent actor in the wider Salafi jihadi movement since the mid-1980s, initially under the auspices of Maktab al-Khidamat.²³ Much of al Qaeda’s worldview and ideology parallels ISIL. But al Qaeda leaders prioritize attacks against the far enemy over the near enemy.²⁴ Al Qaeda leaders also have cautioned their adherents to avoid Muslim casualties whenever possible.²⁵ These divergences are not insignificant. They have caused a rift not only between jihadists on the battlefields of Syria and Iraq but also worldwide. Al-Zawahiri apparently anticipated this rift; in May 2013 he designated an emissary to the conflicts in Syria and Iraq, Abu Khalid al-Suri, in an attempt to resolve these differences. But al-Suri was killed by ISIL fighters in February 2014.²⁶ 

Al Qaeda, in contrast to a more hierarchical ISIL, has retained its networked structure over the years. Often described as a franchise, al Qaeda senior leaders reportedly remain based in Pakistan, but they provide guidance to affiliated militant groups around the world. These affiliates include al Qaeda in the Arabian Peninsula (AQAP), al Qaeda in the Islamic Maghreb (AQIM), al Qaeda in the Indian Subcontinent, and the al-Nusra Front in Syria.²⁷ Additionally, the Khorasan Group, also based in Syria, is comprised of experienced al Qaeda fighters from Afghanistan and Pakistan who traveled to Syria to fight the Asad regime.²⁸ In total, al Qaeda and its affiliates have an estimated 8,700 fighters globally, although it is worth noting that the majority of these fighters exist with affiliated groups, not core al Qaeda.²⁹ Al Qaeda leaders also have established ties to the Taliban, Haqqani network, Tehrik-e-Taliban, and Lashkar-e-Tayyba in Afghanistan and Pakistan. 

The rise of ISIL, its 2014 declaration of a caliphate, and subsequent defections clearly put pressure on al Qaeda leaders to demonstrate their relevance to the wider Salafi jihadi movement, of which both ISIL and al Qaeda are part. They have responded to this pressure by positioning al Qaeda as the most viable alternative to ISIL for those Muslims who do not feel comfortable with ISIL’s tactics on the battlefield. Al Qaeda leaders also have rebuked ISIL for causing disunity within the Salafi jihadi movement. The following joint statement by AQAP and AQIM illustrates this approach: “On top of this the [ISIL] spokesman declared war on all groups and factions everywhere and threatening to fight and shed their blood. This indicated the extent of their deviation and misguidance. Instead of directing their fight towards the enemies of the ummah, and to direct their arrows towards the Jews and Christians, they chose to direct their arrows towards the chests of Muslims.”³⁰ 

Al Qaeda affiliates also have tried to revive their own efforts against the United States and its allies. This has manifested itself in the emergence of new al Qaeda training camps in Afghanistan and attacks by al Qaeda affiliates against Western targets overseas.³¹ These include an attack by AQAP on the office of the Charlie Hebdo satirical magazine in Paris in January 2015 and an attack by AQIM on the Radisson Blu hotel in Mali in December 2015. That said, neither of these attacks reached the level of death, injury, or damage as those conducted by ISIL fighters. 

Will al Qaeda fully reemerge in 2017? Will al Qaeda join with ISIL to form a united transregional network? Will this united network pose an even greater threat? These are the questions being asked by terrorism analysts today. The answers will likely depend on the extent to which the United States and its partners can maintain pressure on ISIL and al Qaeda’s transregional networks simultaneously. Over the past decade, al Qaeda senior and mid-level leaders have been targeted by U.S. and other counterterrorism forces (see figure 2). It is arguable that these and other intensive efforts have diminished al Qaeda’s ability to attack North America, Western Europe, or Australia or even to mount significant attacks on Western targets overseas. But this type of counterterrorism campaign requires concerted resources, including intelligence collection and analysis, law enforcement and diplomatic pressure, and, in many cases, the use of U.S. military instruments, primarily U.S. special operations forces (SOF) and airpower. These resources are finite, and tradeoffs exist. It still remains an open question as to whether the U.S. Government can effectively combat two transregional terrorist networks, as well as maintain its readiness against more conventional state adversaries. The new administration, Democratic or Republican, will have to reconcile these national security priorities. 

Lebanese Hizballah and Lashkar-e-Tayyba 

In addition to ISIL, al Qaeda, and their affiliates, two additional transregional terrorist networks are worthy of note for U.S. national security policymakers. Neither of these networks poses a threat to the United States today, but they should be monitored for shifts in intent and behavior. The first, Lebanese Hizballah, has not threatened the United States directly since the early 1980s. But despite this absence, it often emerges in discussions of transregional terrorist networks that might pose a threat in the future. This is due in part to its relationships with Iran’s Islamic Revolutionary Guard Corps (IRGC), Shia militias in Iraq, the Palestinian Islamic Jihad, and Huthi rebels in Yemen.³² 

Led by Hassan Nasrallah, Hizballah has maintained strong ties to Iran since the 1980s.³³ Originally an actor in the Lebanese civil war, Hizballah shifted its attention to Israel and its forces in southern Lebanon after a power-sharing arrangement was reached for the governance of Lebanon as part of the 1989 Ta’if Agreement.³⁴ Today, Hizballah reportedly has 5,000 fighters under its command in Lebanon with up to 2,000 more deployed to assist President Asad’s forces in Syria.³⁵ Its close ties with the IRGC also provide Hizballah with access to weapons and financing, and, in some instances, the two have been accused of collaborating on terrorist attacks.³⁶ Hizballah’s transregional network also has reach into the United States, albeit in a limited way. In March 2014, for example, Federal Bureau of Investigation (FBI) agents arrested a Lebanese-born American for attempting to travel to Syria to fight with Hizballah; he reportedly received between $500 and $1,000 for his trip.³⁷ 

Lashkar-e-Tayyba (LeT) also deserves some mention as another transregional terrorist network that might pose a threat (albeit much less so than the other networks discussed in this chapter) to the United States and its allies in the future. Based in Pakistan, LeT is led by Hafiz Muhammed Saeed and has a fighting force of between 750 to several thousand.38 LeT has ties to al Qaeda and the Haqqani network, but it also operates its own independent network, stretching from Pakistan to Saudi Arabia to the United States.39 In November 2008, gunmen associated with LeT attacked the Taj Hotel in Mumbai as well as 11 other sites, killing 164 people. U.S. citizen David Headley pleaded guilty in March 2010 to scouting targets for this attack. 

New Dynamics 

The United States also faces two additional counterterrorism challenges: increased numbers of foreign fighters and lone wolves. This section addresses these two threats as they exist now and how they might evolve in the future. 

Foreign Fighters 

As of November 2015, 30,000 foreign volunteers had traveled to Syria and Iraq either to fight against the Assad regime or otherwise support the ongoing battles; an additional 5,000 were believed to be in Libya.⁴⁰ While foreign fighters are not a new phenomenon, these numbers are unprecedented (see table 1). For example, an estimated 20,000 foreign volunteers fought against Soviet forces in Afghanistan between 1980 and 1992; that is an average of 1,650 foreign fighters entering the conflict per year.⁴¹ Similar numbers existed for Operation Iraqi Freedom. Approximately 5,000 foreign fighters traveled to Iraq between 2004 and 2009 to fight against U.S. forces for an average of 1,000 per year.⁴² These averages are hardly comparable to the current conflicts: 7,500 volunteers per year for Syria and Iraq and 2,500 per year for Libya. 

Some debate exists, however, as to the nature and extent of the threat posed by foreign fighters to the U.S. homeland, Western Europe, Canada, or Australia. Most agree that foreign fighters can provide unique skills to terrorist groups, such as medical skills or how best to use social media. But questions remain about how many will return home and whether those who do will conduct attacks there. The latter represents a key concern for Western Europe today. If 30,000 foreign volunteers are in Syria and Iraq, for example, some can be expected to be killed on battlefields. Estimates vary. A report by the Soufan Group suggests that approximately 7 percent have been killed on battlefields.⁴³ A separate report released by the Brookings Institution cites an estimate by European intelligence officials of 20 percent.⁴⁴ By comparison, a report by Al-Manar, the television news source associated with Hizballah, estimates 37 percent.⁴⁵ It is difficult to take numbers from Hizballah—ISIL’s archenemy—too seriously. Nonetheless, if we use the high-range number of 37 percent killed on battlefields, this still leaves 18,800 foreign fighters remaining in Iraq and Syria with an additional 3,150 remaining in Libya. Roughly 15 percent of these are estimated to be from North America, Western Europe, or Australia, equating to 3,293 Western foreign fighters.⁴⁶ 

From a counterterrorism perspective, over 3,000 Western fighters still represents a fairly significant number, given the ease with which they can travel throughout Western countries and the historical difficulties that intelligence and law enforcement have experienced in monitoring them. Clearly not all will return home to conduct attacks or will commit terrorist acts if they do return. But some will. Estimates vary on potential recidivism rates from 9 percent to as high as 60 percent (see figure 3).47 This variance suggests that more needs to be done to understand how foreign fighters travel to conflicts, when and how they return home, and how they will behave upon their return. Abdel Hamid Abaaoud, one of the leaders of the November 2015 attacks in Paris, for example, recruited at least two dozen additional team members to conduct this attack. Seven of the nine attackers were foreign fighter returnees from Syria. Two were Iraqis. But most of the other team members—13 in total—had not traveled to Syria or Iraq to fight, suggesting that returnees represent more of a threat than their initial numbers might suggest because they could recruit others to their cause.⁴⁸ 

Notably, the FBI thus far has managed the risk to the U.S. homeland posed by foreign fighter returnees successfully, while security services in France and Belgium have not done as well. The question for a new administration is whether the FBI can sustain this level of effort within the United States in the mid-term or increase its investigations as more foreign fighter returnees reenter the United States. 

Lone Wolves 

Experts use the term lone wolves to denote residents of the United States who plan or participate in terrorist attacks without direct support or operational guidance from terrorist leaders. Some lone wolves are inspired by conflicts overseas. Others are part of local paramilitary groups, white supremacists, or even environmental activists. Members of the U.S.-based Sovereign Citizen Movement, for example, have targeted local police officers in Arkansas, Connecticut, Florida, Nebraska, New Hampshire, and Wisconsin.49 This section focuses only on lone wolves inspired by transregional terrorist networks, namely ISIL and al Qaeda. 

According to Director James Comey, the FBI had open investigations on suspects associated with or inspired by ISIL in all 50 states as of February 2015.⁵⁰ Recent examples of lone wolf attacks include an attack by two men against an event in Garland, Texas, in May 2015 and the death of 14 people in San Bernardino, California, in December 2015. While some experts dispute the danger to the U.S. homeland posed by foreign fighters, most agree that lone wolves represent a real threat. 

Significant research has been devoted to understanding why the current conflicts have inspired so many lone wolves and attracted so many foreign fighters. Most studies, one way or another, point to the relatively sophisticated social media campaign waged by ISIL.⁵¹ In characterizing this sophistication, experts generally make two key observations. First, while the production of ISIL messages tends to be centralized, the dissemination is diffuse. This means that it is difficult to “shut down” ISIL messaging.⁵² Second, ISIL messages appear to be targeted toward specific audiences, including foreign recruits, as illustrated by its English-language magazine, Dabiq.⁵³ Comey has taken this assessment one step further, arguing that ISIL uses social media platforms to target messages directly to recruits via smartphones.⁵⁴ While less appears to be known about which messages resonate with specific audiences, it seems clear that ISIL’s use of social media has contributed to the increase in plots by lone wolves within the United States. 

Policy Implications 

In summary, the primary terrorist threat to the U.S. homeland, Western Europe, Canada, and Australia today emanates from ISIL; al Qaeda represents a secondary threat; and Hizballah and Lashkar-e-Tayyba represent potential future threats. Given the nature and extent of these threats, the U.S. Government faces three main counterterrorism challenges: how to counter two transregional networks simultaneously, how to anticipate and halt the emergence of new transregional networks, and how to mitigate the danger posed by lone wolves and foreign fighters. These tasks are not easy. But while it is impossible to provide a thorough counterterrorism policy in this chapter, the following steps represent a viable way forward for a new administration. 

First, a new administration should take the opportunity to revisit the access and placement overseas necessary for the U.S. Government to sustain activities against the ISIL and al Qaeda transregional networks, as well as anticipate emerging threats. “Access and placement,” in this instance, refers to the allocation of not only U.S. SOF but also intelligence assets, FBI legal attachés, and other law enforcement personnel, such as Customs and Border Protection and Drug Enforcement Administration officers.⁵⁵ The Barack Obama administration has already taken several steps in this direction by increasing the number of SOF deployed to Syria and Iraq and delaying their withdrawal from Afghanistan.⁵⁶ But given the counterterrorism challenges outlined in this chapter, a new administration is unlikely to be able to rely solely on SOF and airpower. It will also need to leverage even more nonmilitary assets, such as diplomacy, intelligence, and law enforcement. 

Second, a new administration should take the opportunity to revisit the authorities and structure within the executive branch needed to counter ISIL, al Qaeda, or other transregional networks effectively. For example, as a new administration develops a way forward to counter these threats, it may want to request an additional Authorization for the Use of Military Force from Congress. It may also need to revisit intelligence- sharing relationships and partnerships. Equally important, as a new administration devotes more nonmilitary assets toward countering these threats, this will require close coordination across the government. The National Counterterrorism Center could help bring all of the Federal agencies together, but it cannot direct the reallocation of resources toward this fight. Such an effort will need to be undertaken by the White House.⁵⁷ 

Third, the United Nations has undertaken multiple efforts to mobilize the international community against foreign fighter flows. These efforts include Security Council Resolution 2178, passed in September 2014, that requires member countries to prevent their citizens from traveling abroad to join terrorist organizations.⁵⁸ The United Nations also has attempted to work with member states to tighten their legal frameworks against foreign fighter flows, as well as identify any needs for technical assistance, especially with respect to advance passenger information.⁵⁹ A new administration should take the opportunity to broaden this effort so that it focuses on not only outbound travel but also returnees. Specifically, the ceasefire and transition negotiations should address the dilemma of what to do with foreign fighters residing within Syria and Iraq. Some countries, such as Russia, have decided to revoke the citizenship of their foreign fighters. But it is not in the interest of the United States to allow these fighters to remain in Syria or relocate to another conflict. The issue of returnees should receive more diplomatic emphasis, forethought, and planning. Similarly, the United Nations should be encouraged to emphasize the challenges posed by recidivism, to identify lessons learned, and to help member states put programs in place now before they experience an unmanageable surge of returnees. A new administration should prioritize assistance to these efforts, whether it be diplomatic, information- sharing, or providing technical support and resources to member states. 

Fourth and finally, a new administration should conduct a full and thorough review of the U.S. Government’s efforts to counter messaging by ISIL, al Qaeda, and potentially other transregional terrorist networks. This will not be easy. Multiple departments and agencies play a role in what is referred to as public diplomacy, strategic communications, information operations, or counter-messaging. But opportunities exist. For example, defectors from ISIL have begun to speak out. Refugees also have told their stories of horrible treatment and losses, which undermine ISIL’s claim to a legitimate caliphate. And just as social media assists ISIL and al Qaeda, it also can be used to gauge the nature and the extent to which ISIL and al Qaeda messages resonate with local populations around the world. But the U.S. Government must have appropriate authorities, structures, resourcing, and plans to take advantage of these opportunities. 

The United States faces an unprecedented threat from terrorism today, emanating from a combination of transregional terrorist networks, foreign fighters, and the lone wolves that they inspire. Yet this threat does not necessitate that the United States be on a constant war footing. It can be managed. Doing so, however, requires the U.S. Government to prioritize its military and intelligence assets appropriately, coordinate its diplomatic efforts more effectively, and expand the use of law enforcement instruments for combating terrorism not only inside the United States but also overseas.

Notes

¹ See, for example, Jesse Byrnes, “FBI Investigating ISIS Suspects in All 50 States,” The Hill, Briefing Room Blog, February 25, 2015, available at <http://thehill.com/blogs/blogbriefing-room/233832-fbi-investigating-isis-suspects-in-all-50-states>; Molly O’Toole, “Is Whack-A-Mole Working Against al Qaeda?” Defense One, June 16, 2015, available at <www.defenseone.com/threats/2015/06/whack-mole-working-against-al-qaeda/115450/>.

² For a summary of this extensive research, see Paul K. Davis and Kim Cragin, eds., Social Science for Counterterrorism: Putting the Pieces Together (Santa Monica, CA: RAND,
2009); see also Kim Cragin, “Resisting Violent Extremism: A Conceptual Model for Non-Radicalization,” Terrorism and Political Violence 26, no. 2 (2014), 337–353.

³ For additional information on this group, see Michael Weiss and Hassan Hassan, ISIS: Inside the Army of Terror (New York: Regan Arts, 2015). Note that some experts still
believe that al Qaeda poses the greatest threat.

⁴ Note that the Islamic State of Iraq and the Levant (ISIL) lost control over territory in 2016. For further discussion on gauging ISIL control over territory, see Kathy Gilsinan,
“The Many Ways to Map the Islamic State,” The Atlantic, August 27, 2014, available at <www.theatlantic.com/international/archive/2014/08/the-many-ways-to-map-the-islamicstate/379196/>.

⁵ Subsequent sections address the foreign fighter flows into Syria and Iraq in greater detail. For additional references, see Patricia Zengerle, “U.S. Fails to Stop Flow of Foreign
Fighters to Islamic State,” Reuters, September 29, 2015, available at <www.reuters.com/article/2015/09/29/us-mideast-crisis-congress-fighters-idU.S.KCN0RT1VZ20150929>;
Michael Pizzi, “Foreign Fighters in Syria, Iraq Have Doubled Since Anti-ISIL Intervention,” Al-Jazeera, December 7, 2015, available at <http://america.aljazeera.com/articles/2015/12/7/foreign-fighters-in-syria-iraq-have-doubled-since-anti-isil-intervention.html>.

⁶ These numbers do not account for approximately $500 million to $800 million taken from Iraqi state-owned banks. See Guy Taylor, “Islamic State Among ‘Best Funded’
Terrorist Groups on Earth: Treasury Department,” Washington Times, October 23, 2014, available at <www.washingtontimes.com/news/2014/oct/23/isis-best-funded-terroristgroup-earth-treasury/?page=all>; Frank Gunter, “ISIL Revenues: Grow or Die,” Foreign Policy Research Institute, June 19, 2015, available at <www.fpri.org/articles/2015/06/isilrevenues-grow-or-die>.

⁷ “Islamic State Expands into Pakistan with Tehrik-e-Khalifat,” Jane’s Terrorism and Insurgency, January 30, 2015; Lara Jakes, “Who’s Part of the Islamic State? Depends
on Who You Ask,” Foreign Policy, May 21, 2015, available at <http://foreignpolicy.com/2015/05/21/whos-part-of-the-islamic-state-depends-whom-you-ask/>; Charlie Winter, “The Virtual ‘Caliphate’: Understanding Islamic State’s Propaganda Strategy,” Quilliam Foundation, July 2015, available at <www.quilliamfoundation.org/wp/wp-content/uploads/publications/free/the-virtual-caliphate-understanding-islamic-states-propaganda-strategy.pdf>; Aaron Zelin, “New Video Message from the Islamic State: ‘Victory from God and an Imminent Conquest—Wilayat al-Khayr,’” Jihadology.net, May 11, 2015, available at <http://jihadology.net/2015/05/11/new-video-message-from-the-islamic-statevictory-from-god-and-an-imminent-conquest-wilayat-al-khayr/>.

⁸ Abdallah Suleiman Ali, “ISIS Announces Islamic Caliphate, Changes Name,” Pascale al-Khoury, trans., al-Monitor.com, June 30, 2014, available at <www.al-monitor.com/pulse/security/2014/06/iraq-syria-isis-announcement-islamic-caliphate-name-change.html#>.

⁹ Abu Muhammad al-Adnani, “This Is the Promise of Allah,” statement released by al-Hayat Media Center, June 30, 2015.

¹⁰ For more information on territorial gains over time by ISIL, see the excellent maps developed by the Institute for the Study of War, available at <www.understandingwar.org/>; for more information on ISIL’s media campaign, see Aaron Zelin, “Picture or It Didn’t Happen: A Snapshot of the Islamic State’s Official Media Output,” Perspectives on
Terrorism 9, no. 4 (August 2015), available at <www.washingtoninstitute.org/uploads/Documents/opeds/Zelin20150807-Perspectives.pdf>; Ali Fisher, “Swarmcast: How Jihadist
Networks Maintain a Persistent Online Presence,” Perspectives on Terrorism 9, no. 3 (June 2015), available at <http://terrorismanalysts.com/pt/index.php/pot/article/view/426/
html>; Winter.

¹¹ For an account of this and other kidnappings, see James Harkin, Hunting Season: James Foley, ISIS and the Kidnapping Campaign that Started a War (New York: Hachette,
2015).

¹² Ben Hubbard, “Terrorist Attacks in France, Tunisia, and Kuwait Kill Dozens,” New York Times, June 26, 2015, available at <www.nytimes.com/2015/06/27/world/middleeast/
terror-attacks-france-tunisia-kuwait.html?_r=0>.

¹³ Andrew Higgins and Kimiko de Freytas-Tamura, “Paris Attack Suspect Killed in Shoot Out Had Plotted Terror for 11 Months,” New York Times, November 19, 2015, available at <www.nytimes.com/2015/11/20/world/europe/paris-attacks.html?ref=liveblog&_r=0>.

¹⁴ President Barack Obama, in this context, compared ISIL fighters in Fallujah, Iraq, to junior varsity basketball players. See Steve Contorno, “What Obama Said About the
Islamic State as a ‘JV’ Team,” PolitiFact, September 7, 2014, available at <www.politifact.com/truth-o-meter/statements/2014/sep/07/barack-obama/what-obama-said-about-islamic-state-jv-team/>.

¹⁵ For further discussion on the near enemy versus far enemy debate in the wider Salafi jihadi movement, see Gilles Kepel, Jihad: The Trail of Political Islam (London: I.B. Tauris, 2002); Fawaz A. Gerges, The Far Enemy: Why Jihad Went Global (New York: Cambridge University Press, 2005).

¹⁶ For an account of these kidnappings, see Harkin.

¹⁷ Ibid., 176; Hassan M. Fattah and Michael Slackman, “Three Hotels Bombed in Jordan; At Least 57 Die,” New York Times, November 10, 2015, available at <www.nytimes.com/2005/11/10/world/middleeast/3-hotels-bombed-in-jordan-at-least-57-die.html>. 

¹⁸ Liam Stack, “How ISIS Expanded Its Threat,” New York Times, November 14, 2015, available at <www.nytimes.com/interactive/2015/11/14/world/middleeast/isis-expansion.html>.

¹⁹ Subsequent paragraphs discuss the issue of foreign fighters in depth. It is worth noting that as of mid-2016, the number of foreign fighters was estimated to be approximately
27,500, with some departing for home or other conflict zones and others being killed on battlefields.

²⁰ Byrnes.

²¹ Rukmini Callimachi, “How ISIS Built the Machinery of Terror Under Europe’s Gaze,” New York Times, March 29, 2016, available at <www.nytimes.com/2016/03/29/world/europe/isis-attacks-paris-brussels.html>.

²² “Al-Qaeda Names Ayman al-Zawahiri as Osama bin Laden’s Successor,” statement issued on jihadist forums, June 16, 2011, translated and reposted by SITE Intelligence
Group.

²³ Kepel; Gerges.

²⁴ Ibid.

²⁵ Ayman al-Zawahiri, “Letter to Zarqawi on Campaign in Iraq,” July 9, 2005, translated and released by West Point Counterterrorism Center, available at <www.ctc.usma.edu/v2/wp-content/uploads/2013/10/Zawahiris-Letter-to-Zarqawi-Translation.pdf>; Abu Musab al-Suri, “Call for Global Islamic Resistance,” unpublished paper released December 2004/January 2005, translated and posted by SITE Intelligence Group, February 16, 2007; Abu Laith al-Libi, “Confronting the War of Prisons,” as-Sahab Media, May 24, 2007, translated and posted by SITE Intelligence Group.

²⁶ “Militants Kill al Qaeda Emissary in Syria,” Jane’s Terrorism and Insurgency Monitor, February 25, 2014.

²⁷ Some fighters from al Qaeda affiliates have defected to ISIL. See Greg Miller, “Fighters Abandoning al Qaeda to Join the Islamic State, U.S. Officials Say,” Washington
Post, August 9, 2014, available at <www.washingtonpost.com/world/national-security/fighters-abandoning-al-qaeda-affiliates-to-join-islamic-state-us-officials-say/2014/08/09/c5321d10-1f08-11e4-ae54-0cfe1f974f8a_story.html>.

²⁸ When some experts argue that al Qaeda remains the most significant threat to the U.S. homeland, they tend to reference the Khorasan Group. See Bruce Bennett, “Airstrikes
in Syria Also Target Little Known Khorasan Group,” Los Angeles Times, September 23, 2014, available at <www.latimes.com/world/middleeast/la-fg-khorasan-20140923-story.
html>.

²⁹ Estimates for the numbers of al Qaeda fighters come from a variety of sources, including Bennett; see also “Al-Qaeda in Afghanistan is Attempting a Comeback,” Fox
News, October 21, 2012, available at <www.foxnews.com/world/2012/10/21/al-qaeda-in-afghanistan-is-attempting-comeback.html>; “Mapping Militant Organizations,”
Stanford University, available at <web.stanford.edu/group/mappingmilitants/cgi-bin/groups/view/493>.

³⁰ “AQAP and AQIM Give Scathing Rebuke of IS in Joint Statement,” November 1, 2015, translated and reposted by SITE Intelligence Group, November 1, 2015.

³¹ Eric Schmitt and David E. Sanger, “As U.S. Focuses on ISIS and the Taliban, Al-Qaeda Reemerges,” New York Times, December 29, 2015, available at <www.nytimes.com/2015/12/30/us/politics/as-us-focuses-on-isis-and-the-taliban-al-qaeda-re-emerges.html?ref=topics&_r=0>.

³² Sirjah Wahab, “Hizballah Operating in Yemen with Houthis,” Arab News, March 28, 2015, available at <www.arabnews.com/featured/news/724391>; “Palestinian Islamic Jihad,” profile posted by the Government of Australia, available at <>; Mushreq Abbas, “Iran Looks to Iraq for Syria Support,” trans. Joelle el-Khoury, al-Monitor.com, September 13, 2013, available at <www.al-monitor.com/pulse/originals/2013/09/iran-looks-for-support-from-iraq.html>.

³³ For more information on Lebanese Hizballah, see Hala Jaber, Hezbollah: Born with a Vengeance (New York: Columbia University Press, 1997); Naim Qassam, Hizballah: The
Story from Within (London: Saqi Books, 2005); Augustus Richard Norton, Hizballah: A Short History (Princeton: Princeton University Press, 2009).

³⁴ Hassan Krayem, “The Lebanese Civil War and the Taif Agreement,” Digital Documentation Center, American University of Beirut, n.d., available at <http://ddc.aub.edu.lb/projects/pspa/conflict-resolution.html>.

³⁵ As with ISIL and al Qaeda, the numbers for Lebanese Hizballah and its fighting force tend to vary widely. A general consensus appears to be 10,000 from sources. But Tony Badran, at the Foundation for Defense of Democracies, questions these numbers in his blog. He cites a Lebanese intelligence official as estimating a force of 5,000. Similarly, some discrepancies exist on the number of Hizballah forces deployed to Syria, ranging from several hundred to 2,000. For more information, see Tony Badran, “Hezbollah and the Army of 12,000,” April 7, 2013, available at <https://now.mmedia.me/lb/en/commentaryanalysis/hezbollah-and-the-army-of-12000>; Dexter Filkins, “The Shadow
Commander,” The New Yorker, September 30, 2013, available at <www.newyorker.com/reporting/2013/09/30/130930fa_fact_filkins>; Abbas.

³⁶ Kim Cragin, “Hizballah, Party of God,” in Aptitude for Destruction, ed. Brian Jackson et al. (Santa Monica, CA: RAND, 2005).

³⁷ Abha Shankar, “Dearborn Man Arrested Trying to Join Hizballah Fighters in Syria,”Investigative Project Blog, March 18, 2014, available at <www.investigativeproject.org/4318/dearborn-man-arrested-trying-to-join-hizballah#>.

³⁸ The National Counterterrorism Center Web site states that Lashkar-e-Tayyba has several thousand fighters, while the South Asia Terrorism Portal Web site estimates 750.
See “Lashkar e Tayyba,” available at <www.nctc.gov/site/groups/let.html> and <www.satp.org/satporgtp/countries/india/states/jandk /terrorist_outfits/lashkar_e_toiba.htm>.

³⁹ Ibid.

⁴⁰ Zengerle; Pizzi.

⁴¹ The number 20,000 represents a high-end estimate. See Thomas Hegghammer,“The Rise of Muslim Foreign Fighters,” International Security 35, no. 3 (Winter 2010/2011), 61.

⁴² Ibid.

⁴³ Richard Barrett, Foreign Fighters in Syria (New York: Soufan Group, June 2014), available at <http://soufangroup.com/wp-content/uploads/2014/06/TSG-Foreign-Fightersin-
Syria.pdf>.

⁴⁴ Daniel Byman and Jeremy Shapiro, Be Afraid, Be a Little Afraid: Western Foreign Fighters in Syria and Iraq, Policy Paper 34 (Washington, DC: The Brookings Institution,
November 2014), 20.

⁴⁵ “9936 al Qaeda-linked Arabs Killed in Syria,” al-Manar.com, December 24, 2013, available at <www.almanar.com.lb/english/adetails.php?fromval=1&cid=23&-frid=23&eid=126949>.

⁴⁶ The 15 percent comes from estimated totals: 30,000 foreign fighters and 4,500 from the West.

⁴⁷ Byman and Shapiro. 

⁴⁸ These numbers were calculated based on the ratio for the Paris attacks—3 foreign fighters: 10 local recruits.

⁴⁹ The Lawless Ones: The Resurgence of the Sovereign Citizen Movement, Special Report by the Anti-Defamation League, 2nd ed. (New York: Anti-Defamation League, 2012), available at <www.adl.org/assets/pdf/combating-hate/Lawless-Ones-2012-Edition-WEBfinal.pdf>.

⁵⁰ Byrnes.

⁵¹ See, for example, Byman and Shapiro; Winter; Zelin, “Picture or It Didn’t Happen”; Barrett; see also Scott Shane and Ben Hubbard, “ISIS Displaying a Deft Command
of Varied Media,” New York Times, August 30, 2014, available at <www.nytimes.com/2014/08/31/world/middleeast/isis-displaying-a-deft-command-of-varied-media.html?_r=0>.

⁵² Jyette Klausen, “Tweeting the Jihad: Social Media Networks of Western Foreign Fighters in Syria and Iraq,” Studies in Conflict and Terrorism 38, no. 1 (December 2014), 1–22; Fisher; J.M. Berger and Jonathan Morgan, The ISIS Twitter Census: Defining and Describing the Population of ISIS Supporters on Twitter, Analysis Paper 20 (Washington, DC: The Brookings Institution, March 2015).

⁵³ Ibid. See also Zelin, “Picture or It Didn’t Happen.”

⁵⁴ Kevin Johnson, “FBI Director Says Islamic State Influence Growing in U.S.,” USA Today, May 7, 2015, available at <www.usatoday.com/story/news/nation/2015/05/07/isisattacks-us/70945534/>.

⁵⁵ Under the leadership of Admiral William McRaven, U.S. Special Operations Command explored the possibility of establishing what was referred to generally as a “global SOF network.” This proposition came under significant criticism and so did not gain traction among policymakers. This chapter does not advocate a return to the global SOF network, but rather, a more limited presence in the form of a series of Special Operations Command–Forward elements attached to Embassies or consulates. For more information, see Posture Statement of Admiral William H. McRaven, Commander, United States Special Operations Command, before the 113^th Congress House Armed Services Committee, March 6, 2013, available at <http://docs.house.gov/meetings/AS/AS00/20130306/100394/HHRG-113-AS00-Wstate-McRavenU.S.NA-20130306.pdf>; Jack Jensen, “Special Operations
Command–Forward Lebanon: SOF Campaigning Left of the Line,” sidebar in reprint of Michael Foote, “Operationalizing Strategic Policy in Lebanon,” Special Warfare (April–June 2012).

⁵⁶ Jim Acosta and Jeremy Diamond, “Obama Again Delays Afghanistan Troop Drawdown,” CNN, October 15, 2015, available at <www.cnn.com/2015/10/15/politics/afghanistan-troops-obama/index.html>.

⁵⁷ For further discussion on how to improve interagency performance against these types of threats, see Christopher J. Lamb’s chapter on national security reform in this volume.

⁵⁸ Somini Sengupta, “Security Council Passes Resolution to Thwart Foreign Fighters,” New York Times, September 24, 2014, available at <www.nytimes.com/news/un-general-assembly/2014/09/24/security-council-passes-resolution-to-thwart-foreign-fighters/?_r=0>.

⁵⁹ United Nations, “Action Against Threat of Foreign Terrorist Fighters Must Be Ramped Up, Security Council Urges in High-Level Meeting,” Press Release No. 11912,
May 29, 2015, available at <www.un.org/press/en/2015/sc11912.doc.htm>.