Leadership Decapitation
Strategic Targeting of Terrorist Organizations
Jenna Jordan




It is just after 11 p.m. on May 1, 2011. Two Blackhawk helicopters carrying twenty-three Navy Seals from the US Naval Special Warfare Development Group, also known as DEVGRU or Seal Team 6, leave Jalalabad airfield in eastern Afghanistan. Fifteen minutes later, the team crosses into Pakistani airspace. Five minutes from Osama bin Laden’s compound in Abbottabad, Chalk One, the team in Helicopter One, prepares to fast-rope into the compound. The pilot begins to lose control of the helicopter, and it goes down. The assaulters from the Seal team exit the helicopter, jumping about six feet down to the ground. The compound is dark; the power seems to be out.

The team blasts a hole in the gate of the compound’s inner wall and moves inside. They approach the guesthouse, reach a locked door, and blow it open. As they charge the door, the team receives fire from an AK-47. They fire back and call for al-Kuwaiti, bin Laden’s courier, to come out. The door opens a crack and al-Kuwaiti’s wife comes out carrying a child, followed by three children. She tells the Seal team that they have shot her husband. The Seals find al-Kuwaiti’s body and enter the main building, meeting up with a second Seal team that is already inside the building on the first floor. The Chalk One team exchanges fire with al-Kuwaiti’s brother and wife, killing them both.

The two teams then move through a metal gate blocking the entrance to the second floor. Bin Laden’s twenty-three-year-old son, Khalid, who is armed with an AK-47, fires at them. At least two Seals fire back and kill Khalid. Both teams move up to the third floor. Three of the five adult males suspected to be in the compound are still alive. Bin Laden is next.

The Seals blast through another metal door to a staircase leading to the third floor. Their point man sees a man, presumed to be bin Laden, peeking out from a bedroom and fires two shots at him. They enter the room and see two of bin Laden’s wives. Amal al-Fatah, his fifth wife, is yelling, and afraid that she will charge, one of the team members shoots her in the calf. The point man grabs the women and pushes them to the side of the room. A second Seal enters the room and shoots an unarmed bin Laden (capturing or detaining bin Laden had not been seen as an option; the risk of him escaping in a hostile country had been judged to be too great).1

The first phase of the operation, from crash-landing the helicopter to killing bin Laden, has taken eighteen minutes. During the next twenty minutes, four men begin the intelligence-gathering process, collecting flash drives, CDs, DVDs, and computer hardware. The files would reveal that bin Laden was far more involved in the operational aspect of al-Qaeda’s activities than previously assumed. In fact, he had been involved in a number of plans targeting the United States.

The killing of Osama bin Laden is arguably one of the most significant moments in US counterterrorism policy. Shortly after assuming office in January 2009, President Barack Obama directed his new secretary of defense, Leon Panetta, to make “the killing or capture of bin Laden the top priority of our war against al-Qaeda, even as we continued our broader efforts to disrupt, dismantle, and defeat his network.”2 Just after the raid, in his speech to the nation on May 2, 2011, Obama stated, “The death of bin Laden marks the most significant achievement to date in our nation’s effort to defeat al-Qaeda.”3

Immediately after bin Laden’s death, leaders, policy makers, and analysts argued that the organization would be crippled. Bruce Riedel, a former Central Intelligence Agency (CIA) officer and analyst at the Brookings Institute’s Saban Center, argued that, “the death of bin Laden is a very severe blow for al-Qaeda. And it comes at a particularly bad time for al-Qaeda.”4 Given the revelation after the raid that bin Laden had maintained an operational role within the organization, it is unsurprising that policy analysts assumed his capture would devastate the group’s operational capacity. Obama was more cautious in his assessment, arguing that bin Laden’s death would not mark the end of the US counterterrorism effort and that al-Qaeda was likely to continue pursuing attacks against the United States. The administration continued, and increased, its targeting policies. In a May 2013 address to the National Defense University, President Obama announced that instead of conventional military action, targeted operations to dismantle terrorist networks would be a critical aspect of the administration’s counterterrorism strategy. The administration stated a preference for capturing terrorist leaders; however, where this was either not possible or posed considerable risks, as was the case with bin Laden, they argued that targeted killings should be employed. These speeches highlight the tension between the belief that decapitation is an effective counterterrorism policy and the acknowledgement that groups such as al-Qaeda or the Islamic State of Iraq and Syria (ISIS) are likely to continue carrying out terrorist attacks.

States can employ a number of different tactics to defeat and degrade terrorist organizations, including brute force, repression, regime change, negotiations, undermining of support, ideological change, cutting off of finances, and leadership targeting. While all of these measures have been used, leadership decapitation or leadership targeting, which refers to the arrest or killing of a group’s leadership, has become the primary tool in current counterterrorism strategies. The targeting of terrorist leaders has increased substantially since the attacks of September 11, 2001. It was listed first in the priorities of action in the 2006 National Strategy on Combating Terrorism,5 a document framed in terms of countering a broader ideological threat. By 2011, the National Strategy for Counterterrorism was focused less on a strategy of regime change in countries in which terrorist activity emerged and more on the importance of undermining al-Qaeda’s operational capacity. It argued that the threat of terrorism could be eliminated through weakening, disrupting, and degrading al-Qaeda and its affiliates. While the 2011 strategy did not highlight the tactical choices necessary to achieve its broader goals, it argued that US efforts in Afghanistan and Pakistan had destroyed much of al-Qaeda’s leadership and thus substantially weakened the organization. Released just after the death of Osama bin Laden, the document claimed that the group was struggling and faced significant organizational challenges, likely undermining its ability to adapt and evolve.

Terrorist leaders can be targeted in a number of different ways: by strikes fired from aircraft or unmanned aerial vehicles, raids, or the use of special operations forces to capture or kill them. While bin Laden was killed during a raid carried out by US Navy Seals and Abu Muhammad al-Adnani, a leader of ISIS in Iraq, was killed by an air strike, drone strikes have become one of the primary means by which the United States targets leaders. They have a much smaller footprint than a ground invasion and are unlikely to be seen as an occupation. Drone strikes also are considered to be more accurate, result in fewer civilian casualties, and as less likely to cause radicalization, all of which increase the likelihood that decapitation will remain a widely used tactic.6 Most of the strikes in Pakistan, Yemen, and Somalia were against lower-level operatives rather than the upper leadership. While the majority of drone strikes have been carried out in Yemen and Pakistan, the United States has also carried out strikes in Afghanistan, Iraq, Somalia, and Syria, with an increasing number targeting ISIS and al-Qaeda operatives in Iraq and Syria.

The frequency with which the Obama administration used predator air strikes against militants in Yemen and Pakistan demonstrates the prevalence of the belief that targeting leaders is a strategic move and that drone strikes are a low-cost delivery system that minimizes the risk of civilian casualties while precipitating organizational decline. Beginning in 2008, the Obama administration significantly increased the number of drone strikes used to target both high- and lower-level operatives.7 In a few prominent examples, Abu Umar al-Baghdadi, leader of the Mujahideen Shura Council, which later became the Islamic State of Iraq, and Abu Ayyab al-Masri, leader of al-Qaeda in Iraq, were both killed in drone strikes in April 2010 in Iraq. Ilyas Kashmiri, reportedly a senior member of al-Qaeda and the operational commander for Harakat-ul-Jihad al-Islami (HuJI), an Islamist organization largely active in Pakistan, Bangladesh, and India, was killed in a drone attack in South Waziristan on June 3, 2011. Anwar al-Awlaki, a Yemeni-American cleric linked to a number of terrorist plots in the West, was killed in Yemen on September 30, 2011, by a Hellfire missile fired from an American drone.8 In June 2012, Abu Yahya al-Libi, al-Qaeda’s deputy leader, was killed in a CIA drone strike in Pakistan; he was highly experienced and served an important operational function within the organization, and his death was seen as a significant blow to an already weakened al-Qaeda.9 On August 22, 2011, Atiyah Abd al-Rahman was reportedly killed in a drone strike in Pakistan;10 he was believed to be al-Qaeda’s second highest leader and a key link between bin Laden and lower-ranked members of the organization. On June 12, 2015, the leader of al-Qaeda in the Arabian Peninsula, Nasir al-Wuhayshi, was killed by a drone strike in Yemen. While policy makers predicted that these attacks would result in substantial organizational weakening and operational degradation, these groups remain active, and in some cases have become even more so.11

Decapitation is a visible counterterrorism measure that can make a fearful domestic audience feel secure in the belief that their government is winning the war on terrorism and willing to act to keep them safe. The Israelis have utilized this as a powerful tool. Leadership targeting12 can also appeal to the public’s sense of justice and retaliation. For example, scholars have claimed that even though targeting Hamas leaders has neither weakened nor destroyed the group, it appeals to the public’s sense of revenge and justice and enhances the perception of government strength.13 In his May 2, 2011 address, Obama stated that “justice has been done.” After his announcement of the death of bin Laden, crowds formed outside the White House to celebrate.

While it is clear that a large number of attacks against leadership have been successful in killing their intended targets, there is considerable debate regarding the effectiveness of decapitation in destabilizing terrorist groups, as well as its legality and morality.14 Some academics, analysts, and policy makers have found evidence that it is effective, reducing a group’s operational capacity and frequency of attacks, hindering its organizational cohesion, and forcing leadership underground. Others have found that it is ineffective and can have counterproductive consequences, including an increase in retaliatory attacks, a surge in attacks to signal that the group has not been weakened, or an increase in the targeting of civilians as a tactic.15 Further, the death of terrorist leaders can trigger new attacks, either in retaliation or to signal that a group is still strong. Often, groups will call upon their followers to avenge the death of a particular leader, resulting in attacks both claimed and unclaimed.

Despite continued debate over its ability to destabilize and weaken a terrorist group, policy makers continue to argue that targeting leaders is an important part of US counterterrorism policy. For example, immediately following the death of Abu Musab al-Zarqawi, who was killed on June 7, 2006, by a US air strike in Iraq, President George W. Bush announced that al-Qaeda had been dealt a “severe blow.” After the death of al-Masri on April 18, 2010, the Obama administration announced that al-Qaeda had suffered a “major setback.” The day after bin Laden’s death, President Obama stated:

For over two decades, bin Laden has been al-Qaeda’s leader and symbol, and has continued to plot attacks against our country and our friends and allies. The death of bin Laden marks the most significant achievement to date in our nation’s effort to defeat al-Qaeda.16

The state department echoed this assessment in the 2011 Country Reports on Terrorism: “The loss of bin Laden and these other key operatives puts the network on a path of decline that will be difficult to reverse.”17

Analysts have also predicted that leadership targeting will weaken ISIS. For instance, Abu Muhammad al-Adnani, believed to be the second most important leader of ISIS after Abu Bakr al-Baghdadi, was killed by an air strike in Aleppo, Syria, in August 2016. One of the group’s longest-serving top commanders, al-Adnani was a spokesperson in charge of ISIS’s operations outside of Syria and Iraq and was responsible for the recruitment of foreign fighters. Thomas Joscelyn, a senior fellow at the Foundation for Defense of Democracies and senior editor of FDD’s Long War Journal, states that al-Adnani was one of the group’s most senior officials, and probably the most visible.18 His death was considered by analysts and policy makers to be a major blow to the organization.19 Adam Deen, a senior researcher at the Quilliam Foundation, said that ISIS would be “scrambling to find a replacement.”20 He argued that the group was dependent upon personality cults and the charisma of its leaders, and as such, the death of a figure such as al-Adnani would be destabilizing.

But in the months after the assassination, ISIS continued to gain new recruits, hold territory, and carry out attacks. Prior to his death, al-Adnani had stated that while ISIS may experience periods of weakening, the movement is more than its capacity to control territory. It is built upon its beliefs and ideology. He states, “O America. Would we be defeated and you be victorious if you were to take Mosul or Sirte or Raqqa? Certainly not! We would be defeated and you victorious only if you were able to remove the Koran from Muslims’ hearts.”21 This statement reflects one of the theoretical arguments advanced in this book—that the ideology of ISIS or al-Qaeda is not dependent upon leadership, or even territorial control. Rather, ideology, organizational structure, and local support have contributed to their ability to withstand the loss of their leaders.

Al-Qaeda Central and its affiliates suffered periods of decline, but bin Laden’s death did not fatally harm the organization. Ayman al-Zawahiri assumed the leadership of al-Qaeda in June 2011, and the group has continued to franchise with the growth of more affiliates, many of which, such as al-Qaeda in the Arabian Peninsula, continue to operate. ISIS has also undergone a large number of attacks on its leadership since the summer of 2014. While the organization has experienced significant setbacks in its territorial control in Iraq, this is not likely the result of its leaders being killed.

Attacks against al-Qaeda and ISIS show no sign of abatement. It is thus essential to evaluate whether decapitation is an effective strategy, and to examine its potential consequences. To address these concerns, this book poses the following question: Does leadership decapitation work? The primary goal of this book is to determine whether it is a successful counterterrorism policy and to account for the variation in its efficacy, both theoretically and empirically. In doing so, the book will examine the conditions under which decapitation is more or less likely to result in organizational decline and degrade a group’s operational capacity. To do this, I created a dataset that examines 1,276 instances of leadership targeting against terrorist groups from 1970 to 2016.22 Figure 1.1 displays the number of both arrests and killings of terrorist leaders from 1970 to 2016. While there has been a decline over the past few years, this trend is unlikely to reverse itself in any considerable way. This issue is even more salient given US and international efforts to target ISIS leaders.

In order to develop counterterrorism policies that undermine and weaken terrorist organizations, it is essential to identify whether our policies are likely to be effective. If decapitation is unlikely to weaken a terrorist organization or is likely to result in adverse consequences for the types of organizations the United States is currently targeting, then it is essential that counterterrorism policy be rethought.

FIGURE 1.1   Leadership targeting, 1970 –2016

The Argument and Method

This book aims to identify and explain why decapitation works in some cases and not in others. To account for this variation, I argue that a group’s susceptibility to leadership targeting is a function of three factors: (1) organizational structure, (2) popular support, and (3) group type or ideology.23 Leadership decapitation is unlikely to result in the demise of groups that are highly bureaucratized, have high levels of popular support, or are driven by a religious or separatist ideology. Leaders matter less under these conditions, and their removal can often have adverse consequences such as retaliatory attacks or an overall increase in the frequency of attacks. This is the case because, first, bureaucratized terrorist groups are diversified, have a clear division of administrative responsibilities and functions, follow rules and procedures, and are thus more likely to withstand the sudden removal of a leader or leaders. Smaller and younger organizations are less likely to be bureaucratized and are thus more likely to succumb to attacks on their leadership. Second, group type is an important factor in resilience to leadership attacks. Islamist, religious, or separatist groups should be more resilient to targeting efforts because their ideology does not depend upon the leader for its articulation; it is often deeply engrained within the group or the local community.24 As a result, these groups often have more popular support, further increasing their resilience. Third, communal or popular support is essential for the provision of resources and potential recruits necessary for a terrorist group to sustain itself and carry out activity. It provides the basis for group legitimacy, which can increase an organization’s efficiency and resilience. Popular support is essential to a terrorist group’s ability to maintain organizational strength and capacity following an attack on its leadership.

The efficacy of decapitation can be evaluated in a number of different ways. Decapitation can result in organizational weakening, degradation, or complete defeat. Alternatively, targeting efforts can strengthen a group by enhancing its resolve or bolstering support and sympathy from local communities or the larger international community. In some cases, leadership targeting has been effective and has resulted in the decline of an organization. In other cases, it has not only been ineffective but has actually emboldened terrorist organizations. This book examines trends in decapitation to account for whether and when it is an effective counterterrorism strategy.

The database created for this study indicates that, overall, decapitation is not an effective strategy. First, it does not increase a group’s mortality rate and does not result in a significant decline in organizational activity. In other words, groups that have experienced decapitation are no more likely to “die” or end than those that have not had their leaders killed or arrested. While certain types of organizations may have a longer or shorter life span in general, decapitation does not have a statistically significant impact on a group’s survival. Second, the statistical analyses identify the conditions under which decapitation is more or less likely to result in a decline in activity and a group’s life span, accounting for variation in its success. In certain cases, decapitation can result in a decline in a terrorist group’s activity. However, the data reveals that larger, older, Islamist, and separatist groups are less likely to fall apart or experience a decline in activity than other groups—and against the most active organizations, decapitation actually results in an increase in activity. In addition, organizations in more autocratic countries or those with a higher GDP had a higher rate of decline. Taken together, the data demonstrates that while decapitation can be effective in certain cases, overall, it does not shorten a group’s life, decrease its activity and lethality, or bring about its demise, and this is particularly true for certain types of organizations.

Definitions and Scope

There has been ongoing discussion in the literature regarding the meaning of the term terrorism.25 The words terrorism or terrorist organization are laden with emotion and political biases and are subject to multiple understandings. As a result, there is little agreement over a clear and precise definition of terrorism. Even within the US government, there are multiple definitions, with each definition reflecting an agency’s priorities. For example, the US Department of State defines terrorism as “premeditated, politically motivated violence perpetrated against noncombatant targets by subnational groups or clandestine agents, usually intended to influence an audience,”26 while the Federal Bureau of Investigation calls it “the unlawful use of force and violence against persons or property to intimidate or coerce a government, the civilian population, or any segment thereof, in furtherance of political or social objectives,”27 and the Department of Homeland Security and the Department of Defense define it as “the calculated use of unlawful violence or threat of unlawful violence to inculcate fear; intended to coerce or to intimidate governments or societies in the pursuit of goals that are generally political, religious, or ideological.”28

In a large and comprehensive study of terrorist definitions, Alex Schmid looked at over one hundred definitions of terrorism in an attempt to find a broad and widely acceptable definition.29 He identified twenty-two different frequently cited definitional elements. In an early influential study of terrorism, Walter Laqueur recognized the challenges in finding a clear and precise definition, and concluded that terrorism is the illegitimate use of force to achieve a political objective by targeting innocent people.30 Bruce Hoffman argues that terrorism is political in its aims, violent or threatens violence, designed to have psychological impacts beyond the target, perpetrated by a nonstate entity, and conducted by either an organization, an individual, or a group of individuals.31 He concludes that terrorism is “the deliberate creation and exploitation of fear through violence or the threat of violence in the pursuit of political change.”32 Following Hoffman’s definition, this book defines terrorism as violence, or the threat of violence, directed against civilians and used by a nonstate actor in the pursuit of a political goal. The term political can encompass a wide range of phenomena, such as the establishment of a religious state, revolution, autonomy, independence, societal change, or even maintenance of the status quo.33

Hoffman argues that while terrorism is difficult to define, it is important to distinguish it from other kinds of violence.34 Specifically, he argues that there is an important distinction between terrorist and insurgent organizations.35 Unlike insurgent groups, Hoffman argues that terrorist groups

do not function in the open as armed units, generally do not attempt to seize or hold territory, deliberately avoid engaging enemy militant forces in combat, are constrained both numerically and logistically from undertaking concerted mass political mobilization efforts, and exercise no direct control or governance over a populace at either the local or national level.36

However, these categories are not entirely clear, and there is considerable overlap. For example, some large terrorist groups have features of insurgent organizations and are able to hold considerable amounts of territory or engage with military forces, while other organizations that engage in terrorist activity do not possess characteristics of insurgencies.

This distinction between defining a group as terrorist or insurgent can have implications for understanding theory, policy, and the specific nature of the threat they pose. Moghadam, Berger, and Beliakova argue that there is a tendency to label insurgent groups as terrorist, and this labeling has political implications. They conclude that it is more accurate to call groups insurgent, given that most of the terrorist groups they examined attacked civilians in addition to government, military, and police targets.37 They argue, “It is also important to note that seeing terrorism as an insurgency-related phenomenon will require governments to adjust their counterterrorism policies to better handle the cultural peculiarities of insurgencies.”38 Obscuring this difference could undermine counterterrorism policies by overlooking the many different means by which terrorist groups attempt to achieve their goals.

Many organizations can be classified as both terrorist organizations and insurgent organizations as many insurgent groups have also used terrorism as a tactic. This book includes insurgent organizations that have used terrorism as a tactic in pursuit of their goals, such as Chechen separatists, Sendero Luminoso (the Shining Path), and the Armed Islamic Group of Algeria (GIA). Some of the groups in the analyses have characteristics of insurgencies, while others are smaller, with little to no territory or governance capabilities, and have relied primarily on the use of terrorist tactics.

The statistical analysis in Chapter 4 conducts separate analyses on the largest and most active groups, which are often considered to be insurgent organizations. Moreover, the exclusion of insurgent groups that do not use terrorism should not impact the validity of the findings. Moghadam, Berger, and Beliakova argue that in practice, most insurgent groups use terrorism as a tactic. Focusing exclusively on insurgent organizations, however, would eliminate a large number of organizations that have been subject to attacks on their leadership. Furthermore, there is something distinct and meaningful about a group’s decision to employ terrorism. While acknowledging that it is important to use the label of “insurgent group,” Moghadam, Berger, and Beliakova acknowledge that the label “terrorist” is still useful because once a group decides to engage in violence against civilians, “it crosses a certain moral threshold that sets it apart from other groups.”39 Given these concerns, this project includes both terrorist groups that do not have characteristics of insurgencies and insurgent groups that target civilians in acts of terrorism in addition to other means. This book recognizes that insurgency is an important category, and thus draws upon literature on both terrorism and insurgencies.

The data utilized for this book covers the period between 1970 and 2016. Three case studies—on Hamas, the Shining Path, and al-Qaeda—are used as a way to examine the theory of organizational resilience and evaluate the statistical results. These cases were chosen for a number of reasons, notably because they offer regional and temporal variation as well as variation in group goals. Hamas has been one of the most frequent targets of decapitation, sustaining nearly thirty years of targeting efforts. There is currently a significant amount of debate surrounding this tactic’s efficacy, yet it continues to be treated as an efficient means by which to undermine Palestinian terrorist groups. The case study on the Shining Path is a hard test for the book. At the time of its demise, it was a large and older organization, which should have increased its resilience to targeting efforts. However, earlier instances of leadership decapitation were not effective against the Shining Path; it was not until the arrest of its leader in 1999 that organizational activity significantly declined. As a result, this chapter offers within-case variation in the efficacy of decapitation against the Shining Path. I argue that it was susceptible to organizational destabilization due to the lack of support inherent to ideologically driven terrorist organizations; support for the organization changed over time and can thus account for the disparity in the effectiveness of leadership decapitation against the Shining Path. Finally, al-Qaeda has been a frequent and continued target of leadership attacks, along with ISIS, so it is important to understand the impact this targeting has had on al-Qaeda’s activity in order to assess the impact of past and future counterterrorism policies.


1. Schmidle, “Getting Bin Laden.” There are discrepancies in the accounts of the raid, especially with respect to who actually killed bin Laden. The two primary accounts come from two of the Seals, Mark Owen and Robert O’Neill, and the main difference between these two narratives is over who initially shot bin Laden. See Owen and Maurer, No Easy Day. In O’Neill’s narrative, the point man who initially shot at bin Laden missed, and then O’Neill fired two shots, hitting bin Laden in the head both times. See Bronstein, “The Man Who Killed Osama Bin Laden. . . . Is Screwed.” This contrasts the claim of an unnamed Seal, still active in Seal Team 6, who claimed the point man shot and injured, maybe even killing, bin Laden, and that O’Neill’s shots were mere “insurance.” See Kulish, Drew, and Naylor, “Another Ex-Commando Says He Shot bin Laden.” Bissonnette’s narrative matches that of the unnamed source that the point man shot bin Laden and then Bissonnette and other assaulters entered the room and shot bin Laden in the chest.

2. Phillips, “Osama Bin Laden Dead.”

3. Ibid.

4. Bakshi, “Former CIA Officer Bruce Riedel on bin Laden Death, Pakistan-U.S. Ties and the Afghan War.”

5. The 2006 document also advocates advancing democracy, cutting off sources of funding, and denying the use of a nation as a base of operations. National Security Council, “National Strategy for Combating Terrorism.”

6. The disputes about the effect of drone strikes are varied and divisive. I will explore this debate in much greater detail in the chapter on al-Qaeda. See Jordan, “Data on Leadership Targeting and Potential Impacts for Communal Support.” and Barela, Legitimacy and Drones.

7. For Peter Bergen and Katherine Tiedemann’s data at the New American Foundation, “International Security Data Site.” There are other datasets on drone strikes. For data from the Bureau of Investigative Journalism, see Bureau of Investigative Journalism, “Covert War on Terror.” For data from the Center for the Study of Targeted Killings at the University of Massachusetts, Dartmouth, Institute for the Study of Counterterrorism & Unconventional Warfare, “States Against Nonstate Actors.”

8. Mazzetti, Schmitt, and Worth, “Two-Year Manhunt Led to Killing of Awlaki in Yemen.”

9. Walsh and Schmitt, “Drone Strike Killed No. 2 in Al Qaeda, US Officials Say.” In the aftermath of al-Libi’s death, Peter Bergen wrote that according to senior U.S. counterterrorism officials, Ayman al-Zawahiri was likely the only remaining influential leader in al-Qaeda. See Bergen, “And Now, Only One Senior Al Qaeda Leader Left.”

10. Mazzetti, “C.I.A. Drone Is Said to Kill Al Qaeda’s No. 2.”

11. This book does not address the legal and moral issues related to the use of drone strikes, but rather evaluates whether targeting leaders, through drones strikes or other means, can weaken terrorist organizations.

12. While leadership targeting is often used to refer to the killing of a leader, in this book, leadership targeting and leadership decapitation are used synonymously. Both refer to either the arrest or killing of a leader.

13. David, “Fatal Choices: Israel’s Policy of Targeted Killing.”

14. See Price, “Targeting Top Terrorists: How Leadership Decapitation Contributes to Counterterrorism”; Johnston, “Does Decapitation Work? Assessing the Effectiveness of Leadership Targeting in Counterinsurgency Campaigns”; Langdon, Sarapu, and Wells, “Targeting the Leadership of Terrorist and Insurgent Movements: Historical Lessons for Contemporary Policy Makers”; Mannes, “Testing the Snake Head Strategy: Does Killing or Capturing Its Leaders Reduce a Terrorist Group’s Activity?”; Byman, “Do Targeted Killings Work?”; David, “Fatal Choices”; Freeman and McCormick, “Leadership Targeting of Terrorist Groups: A Strategic Assessment”; Hafez and Hatfield, “Do Targeted Assassinations Work? A Multivariate Analysis of Israel’s Controversial Tactic During Al-Aqsa Uprising”; Honig, “Explaining Israel’s Misuse of Strategic Assassinations”; or Wilner, “Targeted Killings in Afghanistan: Measuring Coercion and Deterrence in Counterterrorism and Counterinsurgency.” Tominaga argues that the results are uncertain, but that in certain cases, targeted killings can have a deterrent effect; see Tominaga, “Killing Two Birds with One Stone? Examining the Diffusion Effect of Militant Leadership Decapitation,” 54–68.

15. Langdon, Sarapu, and Wells, “Targeting the Leadership of Terrorist and Insurgent Movements”; Mannes, “Testing the Snake Head Strategy?”; and Honig, “Explaining Israel’s Misuse of Strategic Assassinations.” See Jordan, “When Heads Roll: Assessing the Effectiveness of Leadership Decapitation,” 719–55, and Jordan, “Attacking the Leader, Missing the Mark: Why Terrorist Groups Survive Decapitation Strikes,” 7–38.

16. BBC, “Osama Bin Laden’s Death: Political Reaction in Quotes.”

17. https://www.state.gov/documents/organization/195768.pdf, 5.

18. King and Hennigan, “Why Islamic State’s Abu Muhammad Adnani Was Much More Than a Spokesman.”

19. Dearden, “ISIS Dealt a ‘Major Blow’ by Death of Spokesman Abu Muhammad al-Adnani in Air Strike Claimed by US and Russia.”

20. https://www.independent.co.uk/news/world/middle-east/isis-abu-muhammad-al-adnani-killed-dead-us-air-strike-syria-intelligence-aleppo-victory-impact-a7218061.html

21. Wright, “After the Islamic State.”

22. This dataset includes only cases in which a leader was successfully arrested or killed; it does not include failed decapitation attempts.

23. In this book, the terms terrorist group and terrorist organization are used interchangeably.

24. It is important to note that there are exceptions to this, but generally this is the expectation.

25. See for example Weinberg, Pedahzur, and Hirsch-Hoeffler, “The Challenges of Conceptualizing Terrorism”; Schmid and Jongman, Political Terrorism; Hoffman, Inside Terrorism; Crenshaw, Terrorism in Context; and Erienbusch, “The Analytical Study of Terrorism: Taking Stock.”

26. United States Department of State, Patterns of Global Terrorism.

27. US Department of Justice and Federal Bureau of Investigation, “Terrorism: 2002–2005,” iv.

28. Joint Chiefs of Staff DOD, “Department of Defense Dictionary of Military and Associated Terms,” 236.

29. Schmid and Jongman, Political Terrorism.

30. Laqueur, The Age of Terrorism.

31. Hoffman, Inside Terrorism.

32. Ibid., 40.

33. While this definition does not exclude state-sponsored terrorist organizations, I do not include such cases.

34. Hoffman, Inside Terrorism, 34.

35. See ibid., 35. Hoffman also discusses guerilla groups as yet another type of organization. I would like to thank Matthew Kocher for suggesting that the difference between the two groups is grounded in strategic choice. Terrorist organizations employ a strategy of punishment, while insurgencies use a strategy of denial. Of course, this definition allows for potential overlap. For example, the PKK uses denial in rural areas and punishment in urban areas. For work on the distinction between terrorist and insurgent groups see Moghadam, Berger, and Beliakova, “Say Terrorist, Think Insurgent: Labeling and Analyzing Contemporary Terrorist Actors”; Metz, “Rethinking Insurgency”; Hoffman, Inside Terrorism, 35.

36. Hoffman, Inside Terrorism, 35.

37. Moghadam, Berger, and Beliakova, “Say Terrorist, Think Insurgent.”

38. Ibid., 12.

39. Ibid., 3.