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date: 09 March 2021

Intelligence and Terrorismfree

  • Erik J. DahlErik J. DahlDepartment of National Security Affairs, Naval Postgraduate School
  •  and David ViolaDavid ViolaThe Center on Terrorism, John Jay College of Criminal Justice


Intelligence scholars and practitioners have analyzed the challenges terrorism presents for intelligence organizations and have debated how intelligence analysts and agencies can best respond to the challenge. The literature on intelligence and terrorism changed following the 9/11 attacks; three schools of thought emerged. Although a large body of literature has developed in recent years, a number of important areas remain in which further research is needed.


Although the literature on intelligence and terrorism has burgeoned since the attacks of September 11, 2001, scholars and practitioners have long studied the challenges that terrorism presents for intelligence professionals. This body of literature can be divided into three schools of thought, into which much of the post-9/11 scholarship can be organized. Even though the scholarly and policy literature on intelligence and terrorism has grown significantly in recent years, a number of areas remain understudied and deserve further research.

As an example of the limits of the literature, more than sixteen years after 9/11, there has been surprisingly little in-depth, empirical work produced on the intelligence aspects of those attacks. Amy Zegart’s Spying Blind (Zegart, 2007a) remains the lone book-length academic study of that intelligence failure; other increasingly dated works such as Posner (2005), Russell (2007a), and Betts (2007) examine the use of intelligence in the case of 9/11, but only as part of broader reviews of American intelligence. This gap in the literature may simply reflect the nature of the information involved. Ranstorp comments, “Few academic studies successfully connect the terrorism and intelligence studies fields as it demands mastery of two relatively inaccessible information and analytical domains” (Ranstorp, 2007, p. 16). The time lag may also not be very unusual in an historical context; after all, Roberta Wohlstetter’s seminal work, Pearl Harbor: Warning and Decision, was not published until 1962, well after the event it studied. But the current lag does suggest that despite a few valuable journalistic works, such as the work by Wright (2006), the 9/11 attacks themselves remain understudied from a scholarly perspective, and that, more broadly, additional work is needed on the use of intelligence in counterterrorism.

As the years since the attacks of 9/11 have passed, there has developed within some members of the intelligence studies community a belief that the subject of terrorism has been sufficiently covered in the literature and it is time to focus on other challenges (Johnson & Shelton, 2013). Most of the major edited volumes published in recent years have few, if any, articles focused on terrorism. The authors of a recent survey of the state of intelligence studies argue that “the idea of halting research on intelligence and terrorism, in the middle of a worldwide struggle against Al Qaeda and its associates, would strike many in the field as short-sighted” (Johnson & Shelton, 2013, p. 112). The intelligence failures surrounding the emergence of the Islamic State of Iraq and the Levant (ISIL), and the rash of ISIL and AQ-inspired terrorist attacks throughout Europe and North America, have driven the point home.

Several authors have produced valuable article- and chapter-length overviews of intelligence and terrorism in the post-9/11 era (e.g., Campbell & Flournoy, 2001; Ball, 2002; Sims, 2007a; Rosenbach, 2008; Builta & Heller, 2011; Allen, 2013; Byman, 2014), and useful research has been done concerning specific issues such as the importance of human intelligence and the need for improved international intelligence coordination. But much of the work in this area remains general in nature, with many articles consisting primarily of a reminder that terrorism is an especially difficult problem combined with a recommendation that intelligence agencies place greater emphasis on certain problems or make greater use of particular analytical or collection techniques, and that they increase their focus on domestic collection. Beyond these generalities, there is little agreement in the literature on what specifically must be done to improve intelligence performance against terrorism, or even on whether significant improvement is possible.

This article focuses primarily on how intelligence scholars and practitioners have viewed the challenges terrorism presents for intelligence organizations, and on how those experts believe intelligence agencies can best respond to the challenge. Because it approaches the subject from an intelligence studies perspective, it does not attempt to review the broader literature on terrorism and counterterrorism. In addition, several important intelligence-related topics are discussed elsewhere in the Encyclopedia, so they are not covered in detail here: intelligence reform and oversight, the debate over how to balance liberty and security in domestic intelligence, the ethics of intelligence work, the continually expanding role of drones in intelligence and counterterrorism, the high profile intelligence leaks by Bradley (now Chelsea) Manning and Edward Snowden, and the use of interrogation and torture.

This article is organized into four sections. The first reviews the literature on intelligence and terrorism produced before the 9/11 attacks. The second section looks at how the literature changed after 9/11, and highlights several areas in which there has been general (although by no means unanimous) consensus. The third section reviews how scholars and policy experts have answered what some consider to be the most important questions in this literature: Why have intelligence agencies failed to prevent 9/11 and other major terrorist attacks, and what must be done to improve their ability to prevent future attacks? Here, there is no consensus, and this section argues that the literature can be organized into three schools of thought, each of which offers a quite different explanation of past failures and prescription for the future: the orthodox school, the intelligence reformist school, and the CIA critics’ school. The final section describes additional questions discussed in the literature, and outlines several areas in which further research is needed.

Literature on Intelligence and Terrorism before 9/11

Although the problem of international terrorism was overshadowed by superpower rivalry during the Cold War, there was nonetheless a significant literature focusing on the challenges terrorism presents for intelligence. This early work contains strikingly similar issues and arguments that have appeared continuously since. Several articles note that the effort to gather intelligence on terrorist groups presents particular difficulties for democracies. Their authors discuss the need for oversight of intelligence activities and the difficult question of where the balance should be struck between protecting civil liberties and ensuring public safety (e.g., Cooper, 1978; Robertson, 1987; Taylor, 1987). Other familiar topics include the need for international coordination in counterterrorism intelligence efforts (Kerstetter, 1979) and the differing roles played by the FBI and the CIA in combating terrorism (Prince, 1989).

In this earlier literature, scholars examine major terrorist attacks, such as the 1983 Marine Barracks bombing in Beirut, Lebanon (e.g., Ofri, 1984; Hof, 1985; Hastedt, 1988; Kennedy & Brunetta, 1994) and the bombing of the U.S. Embassy Annex in Beirut in 1984 (Motley, 1986, 1987) as well as local and municipal police intelligence operations against terrorism and other threats (Bouza, 1976). Their conclusions often sound as if they could have been written much more recently: although good intelligence is a key factor in countering terrorism, it is very difficult to obtain, and policy makers should not expect to receive perfect intelligence on terrorist threats. David A. Charters (1991) urged that policy makers and the public should be educated on the possibilities as well as the limits of intelligence against terrorism.

Several authors view human intelligence (HUMINT) as the most important factor in countering terrorism. James Berry Motley (1987) wrote, “[i]t is human intelligence – clandestine agents, informers – that is the key to coping with terrorism” (p. 169; see also Ofri, 1984; Sulc, 1987). But the American intelligence community, in particular, was viewed as weak in its ability to gain HUMINT on terrorist groups. Motley, for example, notes in a separate article (1986, p. 83) that “the U.S. intelligence community to date has been severely limited in its ability to penetrate international terrorist organizations.”

In an important early article, Shlomo Gazit and Michael Handel (1980) make several arguments: (a) that in the intelligence effort against terrorism, overt collection was the least valuable source; (b) aerial photography was not very important; (c) technical intelligence, including signals intelligence, was of greater importance; but (d) the most important source was HUMINT, including information gained through the interrogation of captured terrorists. They described the concept of “intelligence warfare” against terrorists, in which intelligence works closely with operators and methods such as deception, psychological warfare, and covert operations are used alongside the more commonly discussed intelligence methods of collection and analysis. In a comment that still rings true, they stated that “in counterterrorist warfare more than any other type of war, the intelligence organization itself is in the forefront of military operations; frequently the border between intelligence work and combat activity is blurred” (Gazit & Handel, 1980, p. 131).

The primary message of this pre-9/11 literature was, in the words of terrorism expert Bruce Hoffman, that “the importance of intelligence to anticipate, pre-empt, and respond is paramount” (Hoffman, 1996, p. 219). A few authors in the years before 9/11 were relatively optimistic about the ability of intelligence agencies and analysts to track and counter terrorist groups. Ian Lesser, for example, argued (Lesser et al., 1999) that the increasing reliance by terrorists on modern information technology would introduce new possibilities for monitoring and surveillance. But for the most part, scholars were pessimistic about the future, warning about the growing challenge for intelligence from threats such as nuclear terrorism (Beres, 1997; Badey, 2001) and terrorists using weapons of mass destruction more broadly (Marlo, 1999).

After 9/11: Areas of Consensus

The attacks of September 11, 2001, reconfirmed for many scholars both the importance and the difficulty of obtaining useful intelligence on terrorist groups. Academics, policy experts, and intelligence professionals have produced numerous articles and papers examining the current challenges presented for intelligence by terrorism, and on many issues there is broad agreement in the literature. This section reviews these areas of consensus and points out important disagreements.

Increased Importance of Intelligence

Intelligence is generally understood to have increased in importance and prestige since the 9/11 attacks. David Kahn writes that the war on terrorism “has featured intelligence in a starring role” (2006, p. 134), while, according to Michael Herman, “Intelligence has been riding high since 11 September” (Herman, 2002, p. 227). Policy makers as well as scholars have made the point that the war on terrorism is unusual in that intelligence occupies such a critical part. Michael Hayden, former Director of the Central Intelligence Agency (CIA), described intelligence as being more deeply involved in this war than it has been in any other (Hayden, 2007), and the National Security Strategy of the United States published soon after 9/11 stated, “Intelligence—and how we use it—is our first line of defense against terrorists and the threat posed by hostile states” (National Security Strategy, 2002, p. 30). Former British Prime Minister Tony Blair made the same argument in 2003, calling intelligence “Britain’s first line of defence against terrorism” (Herman, 2004, p. 348). The war on terrorism has even been described as an “intelligence war” (Aid, 2012; Hayden, 2010).

But while the war on terrorism has led to larger budgets for intelligence services and a more prominent role for intelligence in national decision making, this greater attention has brought with it greater expectations, which scholars argue the intelligence communities of the United States and other nations are finding it difficult to meet. According to Kahn, “intelligence gathering and analysis are now considered such indispensable government functions—and so much is expected of them—that their inability to disperse the fog of war or of international politics causes outrage” (2006, p. 134).

Additional challenges for intelligence agencies have been created because at the same time that public attention is being focused on intelligence, the struggle against international terrorism has placed more emphasis on the aspects of the intelligence business that are the most secret, such as covert operations and espionage (Herman, 2004; Kibbe, 2007). The lines separating military operations, law enforcement, and intelligence operations are becoming more blurred, creating new operational, legal, and organizational difficulties (Best, 2003; Jenkins, 2006a) as well as ethical dilemmas (Olson, 2008). Charles Cogan writes that intelligence operatives of the 21st century will have to be more like hunters than gatherers: “They will not simply sit back and gather information that comes in, analyze it and then decide what to do about it. Rather they will have to go and hunt out intelligence that will enable them to track down or kill terrorists” (Cogan, 2004, p. 317). This job, he predicts, will be largely one for the military special forces community, with intelligence services such as the CIA relegated to a supporting role. Cogan’s prediction was born out in the U.S. SEAL Team raid that killed Osama bin Laden; the operation was legally conducted by the CIA as a covert action, but in practice it was planned and conducted by the special operations community (Dahl, 2014a).

Among the most useful sources on the intelligence effort that led to the killing of bin Laden are Bergen (2012), Schmitt and Shanker (2011), and Mudd (2013). That operation was the most prominent example of what some have described as a new type of intelligence cycle for counter-terrorism: “finding, fixing, finishing, exploiting and analyzing targets,” or F3EA (Builta & Heller, 2011, p. 6). In this version of the intelligence cycle, intelligence is used to drive operations against a terrorist target, allowing analysts to locate the target (find), identify its precise location (fix), and enable operational personnel to capture or kill the target (finish). This in turn produces intelligence on new targets that can be exploited and analyzed, and so on.

Terrorism Is a More Difficult Problem

Although terrorism is not the only important mission for intelligence services in the 21st century, it is widely considered to be the top priority for Western intelligence services. And most scholars and experts believe it is an especially difficult problem for intelligence to deal with. James Hansen puts it starkly: “The al-Qaeda network is believed by some to be the most difficult intelligence adversary the U.S. has ever faced” (2004, p. 692). The intelligence systems and techniques developed during the Cold War are seen as inappropriate for countering terrorists. Fritz Ermarth notes (2002) that “[g]athering intelligence on terrorists is a far more difficult task than assessing whether a strategic rival is planning a massive military attack on the United States. By nature, the terrorist works by stealth, avoiding targets for which elaborate military-style preparations are necessary.”

American intelligence officials have argued that the nature of the intelligence problem is dramatically different and more difficult today. Former Director of National Intelligence Michael McConnell notes that in dealing with a conventional military threat, there is relatively little problem determining the enemy’s capability—his order of battle. With a conventional foe, the enemy’s intent is the question. But in the case of terrorism, McConnell argues, “it’s just the opposite.” Here the intent to commit harm is clear, and the challenge for intelligence is to learn the enemy’s capability to do so (McConnell, 2007). Then-CIA Director Michael Hayden points out another difference between the problems faced by the intelligence community in the Cold War and today. During the Cold War the enemy’s forces, such as troop formations, tanks, and ballistic missile silos, were relatively easy to find, but hard to kill. Today, on the other hand, “the situation is reversed. We are now in an age in which our primary adversary is easy to kill, but hard to find” (Hayden, 2007).

Gregory Treverton argues (2009, 2010) that terrorism is a more challenging problem for intelligence because it presents a mystery, to which there is no easy answer, rather than a puzzle, which can at least in theory be solved. During the Cold War, U.S. intelligence was charged with finding answers to puzzles such as determining how many missiles were in the Soviet inventory. But today intelligence agencies are finding it much more difficult to solve mysteries: What is the continuing nature of the threat from al-Qaeda? What threat does ISIL pose to the homeland? And what does the future of domestic terrorism from the (ideologically) far right and other groups pose? Because traditional intelligence threat assessments are more difficult to produce, many intelligence and security officials have begun to use vulnerability based assessments that start by identifying one’s own vulnerabilities and then develop scenarios the enemy may follow. Jenkins (2006b, 2006c) points out that such scenarios can take on a life of their own, appearing to produce inevitable and unstoppable threats that may not really exist.

Importance of Domestic and Local-Level Intelligence

Although most studies of intelligence and terrorism focus on the national or international level, a number of authors have pointed out that much of the critical intelligence work is done at the internal, domestic level, by local police and state and regional law enforcement authorities (Peterson, 2005; Riley et al., 2005). Stella Rimington, the former head of Britain’s domestic intelligence organization MI5, writes that terrorism intelligence is not developed by spies overseas as often as one may expect: “My own experience is that effective counter-terrorism frequently begins closer to home and may appear a lot more mundane” (2005, p. 30).

Local police departments may be the first to detect indications of an active terrorist cell, as has been the case several times since 9/11 in cities such as New York (the Herald Square plot in 2004 among others), and hospitals may find themselves on the front lines of a biological attack, as they were during the stateside Ebola scare of 2014. For that reason communications systems and common procedures need to be established that link law enforcement agencies with each other, with potential first responders and with intelligence services (see Hulnick, 2005; Jenkins, 2006a, 2006b; Sims, 2007a). In the United States, significant steps have been taken since 9/11: (a) a proliferation of Joint Terrorism Task Forces (JTTFs) and state and local intelligence fusion centers, (b) the posting of local intelligence officials alongside national-level counterparts at the National Counterterrorism Center (NCTC), and (c) the re-emergence of robust police intelligence operations in New York City and elsewhere (Sullivan & Wirtz, 2008; Svendsen, 2012; Apuzzo & Goldman, 2013; Dahl, 2014b).

The new requirements of countering terrorism at home are driving new methods and models of collection and analysis. Bruce Berkowitz argues that intelligence for homeland security requires a type of tradecraft very different from the old CIA model in which the government secretly collected highly sensitive information from hostile countries and unsavory characters. “The business model for a homeland intelligence agency (if we had one) would sound something like: ‘Collect as much information from as many sources as possible, respect the civil liberties of Americans, and get the product to hundreds of thousands of local officials, public safety officers, and first responders so they can anticipate threats and respond effectively’” (Berkowitz, 2004, pp. 3–4).

Increased domestic intelligence collection presents the opportunity for abuses and violations of civil liberties, as occurred in the 1960s and 1970s with, for example, the FBI’s excesses during the COINTELPRO operations. Commentators such as Marrin (2003) note that homeland security intelligence requires new and greater forms of oversight, like those that emerged from the class-action lawsuit against NYPD’s intelligence service during the 1970s, which resulted in the so-called Handschu agreement limiting intelligence collection by that local agency. In addition, coordination between intelligence and law enforcement is not easy, in large part because the cultures of the two communities are very different and because of real and perceived legal separations between domestic and international intelligence activities (Treverton, 2003; Waxman, 2009).

International Intelligence Cooperation

Several authors have noted that because terrorism today is an increasingly international threat, counterterrorism efforts must be international as well. As Stephen Lander (2004) puts it, “a threat that operates virtually irrespective of nationality and national borders poses particular challenges for intelligence services and for international collaboration between states” (p. 482).

The importance of intelligence liaison relationships for counterterrorism was recognized well before 9/11 (e.g., Motley, 1986), but such arrangements are becoming increasingly important today in what Michael Herman calls the “internationalization” of intelligence (2004, p. 349–350). Useful discussions of the issue include particularly Walsh (2010), as well as Rudner (2004), Sims (2006), Svendsen (2008), Lefebvre (2003), Segell (2004), Lansford (2007), and Stevenson (2006). Nomikos (2005), Norell (2007), and Den Boer (2015) focus on European intelligence cooperation. Not everyone believes, however, that intelligence efforts have yet become sufficiently “international.” Mackmurdo (2007), for example, argues that international intelligence relationships and trust among intelligence services are lacking today. He suggests that the United Nations, in particular, needs to develop an effective intelligence capability to combat international terrorism.

Concerning the United States, Richard J. Aldrich (2002) notes that even the world’s largest intelligence system cannot go it alone in the effort against international terrorism, as “despite its size, the United States finds itself dependent to some degree on intelligence alliances with middle power allies. It produces more intelligence but also has a vast appetite. It is a massive exporter of technical intelligence while it is also surprisingly dependent on friends for certain kinds of espionage” (p. 54). Derek S. Reveron (2006) points out that, in the United States since 9/11, most of the discussion about intelligence sharing has focused inward—on improving information sharing within the U.S. intelligence community. He argues that greater attention should be paid to the need for U.S. intelligence agencies to establish cooperative international relationships, especially bilateral agreements that may take advantage of another country’s comparative intelligence advantage in a particular geographic region or against a certain target. And Daniel Byman (2017) reviews the many difficulties involved with international intelligence cooperation, describing liaison relationships as “a vital but imperfect weapon in the US counterterrorism arsenal” (p. 155).

Human Intelligence Is Increasingly Important

Many experts believe that the most important source of intelligence on terrorist groups is human intelligence (HUMINT). Human intelligence is not seen as the complete answer to the problem of terrorism, of course, and some authors argue that other sources can be very useful, such as signals intelligence (Aid, 2003), or open source intelligence (Sloan, 2006; Lewis & Chenoweth, 2007). It is also frequently pointed out that other types of intelligence community improvements are needed, such as increasing the numbers of interpreters and officers with critical language skills, developing databases to handle the new information, and experimenting with new (and often not-so-new) analytic methods such as red-teaming (see, e.g., Campbell & Flournoy, 2001). But the most commonly heard argument is that technical intelligence collection methods such as imagery intelligence (IMINT) and signals intelligence (SIGINT) are not very useful against terrorist targets, while HUMINT is critical.

Brian Jenkins (2003) expresses this view in his testimony before the 9/11 Commission: “Using intelligence to prevent terrorist attacks is very difficult. There are no troop mobilizations to watch for, no ships, no aircraft to track. Knowing what terrorists may do depends largely on human sources—undercover agents and informants. Penetrating small terrorist groups may take months, years.” As Jenkins indicates, human intelligence is something of a dilemma for intelligence agencies, as on the one hand it is critical in the fight against terrorism, but on the other hand it is extremely difficult to obtain (see also Lewis, 2004; Betts, 2007; Weiner, 2007; and an insightful first-hand account in Crumpton, 2012).

Some are skeptical about the belief that increased HUMINT is the answer. Mark V. Kauppi (2006, p. 424) notes that placing American agents within terrorist groups is very difficult, even if the agent is a native-born speaker of the local language, because many terrorist groups are clan or tribally based. Michael Herman (2003) argues that “even the best HUMINT—and the extensive liaison with foreign services it often entails—will not provide a magical solution on targets of the Al-Qaeda kind” (p. 44). Frederick P. Hitz (2005) writes that recruiting agents (spies) is harder today than it used to be: “In the war on terrorism, the spies will surely be harder to get at than during the Cold War. Their religious, ethnic, and cultural differences from Western spy-runners, and the tight bond of their terrorist commitment, will assure this fact” (p. 731). Several former CIA operations officers have also written about the difficulty terrorism poses for American human intelligence operatives. In a comment written before 9/11 but often cited since those attacks as an illustration of how the CIA has been too risk-averse and bureaucratic, Reuel Marc Gerecht (2001) quotes a CIA case officer as saying: “Operations that include diarrhea as a way of life don’t happen” (p. 40).

One way for intelligence services to address this difficulty may be to expand their use of nontraditional types of human intelligence collection. Richard Russell argues that the CIA “needs to break its umbilical cord to U.S. diplomatic facilities overseas as its primary infrastructure for human intelligence collection.” Instead of relying almost completely on case officers based under diplomatic cover at embassies, he believes, U.S. intelligence must substantially increase its use of officers under nonofficial cover—known as NOCs (Russell, 2004, p. 61; see also Russell, 2007b; Berkowitz, 2002b). Jennifer Sims (2007b) challenges the notion that traditional human intelligence is of little use against terrorist targets. She writes, “the conventional wisdom that human intelligence against terrorist adversaries must operate principally outside traditional diplomatic circles is wrong. Classic modes of collection, including official cover, are crucial to detect and counter state sponsorship of terrorism and to work with foreign agencies engaged in domestic intelligence and law enforcement at the local level” (p. 414). She also argues that the most effective method of collection on terrorism is through a synergistic effort, using technical means as well as human sources (Sims, 2005, p. 55). John Deutch and Jeffrey H. Smith (2002) make the similar point that cooperation between human and technical intelligence makes both stronger, as human sources can provide collectors with access they need to gather signals intelligence, while signals intercepts can help to validate information reported by human sources. Numerous scholars, including Carter, Chermak, Carter, and Drew (2014) have found that human intelligence employed by law enforcement is particularly important in combatting terrorism at the domestic level.

Intelligence Performance against Terrorism: Differing Schools of Thought

One of the most enduring puzzles surrounding the 9/11 attacks continues to be: why had the attacks not been anticipated and prevented, even though American intelligence agencies and others had been warning for years about the threat from bin Laden and international terrorism? James Wirtz puts the puzzle this way: “Even accounting for hindsight, it is difficult to understand how the government, the public, and the scholarly community all failed to respond to the threat posed by al Qaeda, in a way that is eerily similar to the failures that preceded Pearl Harbor” (Wirtz, 2006, p. 56).

There is, of course, no single, universally accepted explanation for what went wrong in the months and years preceding 9/11. Some, especially from within the intelligence community, have argued that the attacks were not the result of an intelligence failure. Some analysts and scholars take a macro view, arguing that blame for 9/11 must be assigned more widely than just to the intelligence community. Joshua Rovner, for example, writes, “September 11 was not an intelligence failure, it was a national failure” (Rovner, 2005, p. 3). Others take a micro view, that the attacks were the result of individual incompetence or bad decisions (e.g., Anonymous [Scheuer], 2004; Clarke, 2004).

Nonetheless, the attacks on 9/11 have been widely seen as an intelligence failure unmatched by any in American history since Pearl Harbor. In addition to the debate on who should bear the responsibility for that intelligence failure, more broadly the question also remains of how well has the U.S. intelligence community has performed against terrorism in general. Much of the literature since 9/11 has attempted to answer these questions and to explain what the U.S. intelligence community (and to a lesser extent, the intelligence services of other nations) can or should do to prevent future attacks. This literature can be divided into three schools of thought, each of which offers a distinct analysis of what has gone wrong in the past and what should be done in the future. (Similar typologies are provided in Parker & Stern [2005], and Copeland [2007].) Although not all scholars and experts fit neatly into this model, these three schools help explain the different approaches taken in the literature.

The most prominent school of thought concerning terrorism and intelligence is also the most pessimistic. These thinkers, in what has been termed the orthodox school, are the intellectual heirs of earlier literature that examined the reasons why conventional military surprise attacks almost always succeed (e.g., Wohlstetter, 1962; Handel, 1977; Betts, 1978; for discussion of the orthodox school, see Honig, 2008). Following much the same logic as the earlier literature, and indeed often including the same thinkers, the orthodox school argues that intelligence failures such as 9/11 are largely unpreventable, and that while some improvements to intelligence are possible, the best policy option is to assume that surprise attacks like 9/11 or the 2013 Boston Marathon bombing will often succeed and prepare to deal with their effects. This school includes a number of well-known writers and thinkers about intelligence (e.g., Pillar, 2003; Heuer, 2005; Hedley, 2005; Betts, 2006). These thinkers believe that the U.S. intelligence community has generally done a good job, even in the years and months leading up to 9/11, especially in terms of strategic intelligence by providing a broad, long-term warning of the rising threat from terrorism and from al-Qaeda in particular. They argue that if anyone is to be held accountable for disasters such as 9/11, it should be the policy makers for having failed to take heed of the intelligence warnings they were provided (Marrin, 2011).

The collection of more precise intelligence may possibly have helped to prevent the attacks, but these orthodox thinkers point out that having more intelligence can just make the problem of analysis more difficult: “The more dots there are, the more ways they can be connected—and which way is correct may become evident only when it is too late, when disaster clarifies which indicators were salient” (Betts, 2007, p. 105). Intelligence analysis with regard to 9/11 was faulty, according to this view, largely because it put too much emphasis on developing tactical level intelligence, which analysts and officials fail to realize will rarely be available. Ephraim Kam, for example, writes that, prior to 9/11, “Intelligence was more oriented toward tactical analysis in support of operations than on the strategic analysis needed to develop a broader understanding of Al Qaeda and the threat it posed” (Kam, 2004, pp. xviii–xix).

Other scholars and analysts take a less pessimistic view than the orthodox thinkers. They argue that changes can be made to the intelligence community to significantly improve its ability to prevent terrorist attacks. This school of thought, which may be called the intelligence reformist school, is expressed most prominently in the 9/11 Commission Report (National Commission on Terrorist Attacks upon the United States, 2004) and in the work of scholars such as Amy Zegart (e.g., Zegart, 2007a, 2007c). This view sees the surprise aspect of the attack as having been caused largely by preventable analytical and communications failures on the part of the intelligence community and policy makers who lacked the imagination to “connect the dots” (as the 9/11 Commission famously argued) and to make sense of the information that had been available (National Commission on Terrorist Attacks, 2004, p. 408).

Reformists believe that the likelihood of future failures can be reduced by intelligence reforms along lines that have been proposed for the past 50 years—which often stress organizational change—and by efforts to ensure that decision makers take heed of intelligence warnings. While the orthodox thinkers believe that the intelligence community has done a good job in an almost impossible task, the reformists argue that American intelligence agencies have done a much poorer job than they should have. This view is expressed by the title of an op-ed by Amy Zegart in the Los Angeles Times: “American Intelligence—Still Stupid” (Zegart, 2006). Zegart argues that, years after 9/11, the intelligence community remains disorganized, lacks central direction, and duplicates much of its efforts.

According to reformists, American intelligence agencies prior to 9/11 had been too focused on the tactical level and did not produce enough broad, long-range, strategic-level intelligence assessments on the threat from bin Laden and al-Qaeda. Unlike orthodox school thinkers, who believe the U.S. intelligence community did a good job in terms of strategic intelligence, the reformist school holds that if intelligence officials had done a better job of assembling the available warning signs into strategic assessments for senior policy makers, the attacks may have been preventable (see, e.g., Steinberg et al., 2003; Bazerman & Watkins, 2004; Zegart, 2007b.)

Intelligence reformists tend to agree with the orthodox school that intelligence warnings are usually available prior to major failures. They believe that the major problem is that intelligence is not sufficiently shared and coordinated within the vast intelligence community and government bureaucracy.

A third school of analysts and scholars argues that terrorist attacks have succeeded because terrorism presents a dramatically new and different threat against which our intelligence and national security organizations have not been prepared. Many of these writers focus on mistakes and failings of the Central Intelligence Agency, so this school may be called the CIA critics’ school. According to this view, prior to 9/11 the CIA and its Directorate of Operations (DO) that managed human intelligence failed to place enough emphasis on developing human intelligence sources on al-Qaeda and other terrorist groups (Jenkins, 2003; Gerecht, 2004; Berkowitz, 2005; Baer, 2005). Former CIA officer Gerecht (2004, p. 1) describes the principal problem as “the failure of the CIA to develop a clandestine service with a methodology and officers capable of penetrating the Islamic holy-warrior organizations in Europe, the Middle East, and elsewhere.” In the words of Robert Baer, also a former CIA officer (2005, p. 66), “Not to be too blunt about it, but if the DO had a source close to Osama bin Laden, 9/11 would not have happened.”

The CIA critics’ school argues there was not enough intelligence to have anticipated and prevented the attacks. The failure was not primarily one of analysis or of an inability to share information that was already in the system. The failure of 9/11 was a failure of intelligence collection. In the words of The Economist (2003, p. 30): “There were too few useful dots.” The critical problem leading to a lack of intelligence collection on the threat was the failure of the U.S. intelligence community—and particularly the CIA—to place enough emphasis on developing human intelligence sources on al-Qaeda and other terrorist groups. Reuel Marc Gerecht expresses this view in arguing that the example of John Walker Lindh demonstrates that it was possible for Americans to penetrate al-Qaeda. Before 9/11, the CIA never tried to develop their own John Walker Lindh, “Yet even one such source could have obviated any need for Washington to ‘connect the dots’” (Gerecht, 2004).

What Is the Root Cause of the Problem for Intelligence?

Although the orthodox school believes the immediate cause of failure is analytical, for these thinkers the more fundamental cause lies in the limits of human cognition and psychological factors such as an overreliance on preconceived assumptions (on these cognitive problems, see Byman, 2005; Parker & Stern, 2002, 2005). The emphasis on cognitive and psychological factors helps explain why this school of thought tends to see intelligence failure as largely unavoidable. Just as human nature and patterns of cognition are resistant to change, psychological limitations on intelligence are resistant to improvement. Betts, for example, notes in his classic statement of the orthodox approach to intelligence failure that “[u]nlike organizational structure . . . cognition cannot be altered by legislation” (Betts, 1978, p. 83).

For reformist thinkers, the fundamental problem underlying the inability of the intelligence community to share and process information properly lies at the level of structure and organization. Amy Zegart, for example, argues that the CIA and FBI missed 23 potential opportunities to disrupt the 9/11 attacks, largely because organizational routines and cultures were resistant to change, and because intelligence and national security organizations were unwilling to adapt to the development of new threats. “While individuals made mistakes, organizational deficiencies were the root cause of 11 September” (Zegart, 2007b, p. 43).

For thinkers in the CIA critics’ school, the fundamental problem is that terrorism is a more difficult threat than intelligence and national security agencies have previously had to deal with. This is partly because terrorist groups have “smaller signatures” than the nation-state enemies of the past, and because terrorists practice deception. Many in this group argue that America and the world are facing a new type of warfare; Bruce Berkowitz, for example, writes that the 9/11 attacks were “an act of military genius—and may well foreshadow the next era of warfare” (Berkowitz, 2002a, pp. 291–292; see also Shultz & Vogt, 2003).

What Should Be Done?

Most observers of the American intelligence community agree that some sort of change is needed if intelligence agencies are to cope satisfactorily with the threat of terrorism. But much of the advice offered may be difficult to put in practice, such as the call for the intelligence community to “become as agile and as innovative as its terrorist adversary” (Harris, 2002, p. 13).

The three schools of thought offer strikingly different prescriptions for the future of intelligence. Scholars in the orthodox camp tend to be the most cautious about calls for major reform, and they argue that dramatic change is neither needed nor helpful. Paul Pillar, for example, argues that the U.S. intelligence community has been working hard on the problem of international terrorism since at least 1986, when the CIA’s Counterterrorist Center was established. The FBI and municipal police departments have been combatting domestic terrorism for even longer, developing intelligence on and infiltrating terrorist organizations on the political right and left as far back as the era of anarchism and more recently during the tumultuous 1960s and 1970s.

Since 9/11, the number of analysts working on terrorism has increased, but Pillar believes this change is less significant than it looks—and in fact may be reducing the quality of intelligence available. “A surge in the number of analysts assigned to counterterrorist components meant analysts were almost stumbling over each other in turning out large numbers of papers, only a tiny proportion of which could be expected to be of real use in heading off the next major attack” (Pillar, 2007, p. 156). The best way to improve the intelligence community’s “batting average” against terrorist attacks, according to this view, is to improve the quality of intelligence analysis, first by improving the selection and training of analysts, and second by doing a better job of long-term, strategic-level analysis (Betts, 2002).

The orthodox view is a pessimistic one. Because the reasons for failure today are largely the same as in the past, orthodox scholars argue that there seems little reason to believe that the current generation of intelligence officials will be more successful in avoiding surprise than their predecessors were at avoiding surprise attacks such as Pearl Harbor.

Other observers—many of whom can be associated with the intelligence reformist school—believe that dramatic change is needed in the structure, operations, and culture of intelligence agencies. Reformist thinkers tend to be more optimistic than orthodox thinkers about the prospect for significant improvement in intelligence capabilities against terrorism, possibly because the organizational problems they see at work appear to them to be more correctable than the orthodox perceive psychological and cognitive problems to be. Some reformists focus on improving the systems, networks, and procedures used to process and analyze information within the intelligence community (Kamarck, 2005). But the most common call—most notably by the 9/11 Commission—has been for greater centralization of the American intelligence community, leading to the creation of what has become the Office of the Director of National Intelligence.

Other reformists believe that the intelligence community needs to be less centralized, adopting structures more akin to networks, with flatter hierarchies. Jennifer Sims and others argue that the push for greater centralization is misguided because the future of conflict and warfare is leading toward network structures and decentralized enemies, and it takes a network to fight a network (Sims, 2005; see also Arquilla & Ronfeldt, 2001; Barger, 2005; Cronin, 2005; Atran, 2006).

Thinkers in the reformist school do not argue that the necessary changes will be as easy as simply changing the line-and-block organizational diagrams of intelligence communities and individual intelligence agencies. Effective change will require, according to this view, reforming the basic culture of intelligence organizations (Barger, 2005; on the culture of intelligence organizations see Davies, 2004, and Johnston, 2005). And it may require an even more dramatic and fundamental change. Some thinkers argue that the new threats since 9/11, combined with changes in information technology and in the nature of warfare, require nothing less than a “revolution in intelligence affairs” (Barger, 2005; see also Lahneman, 2007).

Thinkers in the CIA critics’ school often advocate greater use of covert operations and preemptive military force against terrorist targets, but the major recommendation from this school is for increased emphasis on human intelligence. The Economist, for example, argues (2003, p. 30) that the focus on improving analysis found in much of the discussion about intelligence reform “distracts attention from the real need: improved espionage, to provide the essential missing intelligence.” The best way to do it, the magazine’s editors argued, is to place spies within the “innermost councils” of terrorist organizations. But writers in this school are often gloomy about the prospect for change in American intelligence, largely because they do not believe the CIA will be able or willing to make the changes needed. Gerecht (2006, p. 3), for example, writes, “Regrettably, reform at the CIA is now dead.”

Additional Topics and Gaps in the Literature

Although the topics reviewed here are some of the most commonly discussed issues in the literature on intelligence and terrorism, many authors have focused on more specific questions. Some have examined the use of intelligence in countering particular types of terrorist threats, such as nuclear (Zenko, 2006; Mowatt-Larssen, 2009), biological (Enemark, 2006), chemical (Pita, 2007), or cyber terrorism (Gosler, 2005; Rudner, 2013; Wirtz, 2014). The American intelligence community’s poor performance in assessing Iraq’s weapons of mass destruction programs suggests to some that the community may not be up to the task of countering weapons of mass destruction (WMD)–armed terrorist adversaries (e.g., Russell, 2005).

Recommendations for intelligence agencies in the effort against terrorism include greater focus on tracking terrorist finances (Rudner, 2005; Williams, 2005; Winston, 2007), increased monitoring of terrorist related Internet sites (Renfer & Haas, 2008), and more emphasis on the broader themes and messages of propaganda from groups such as al-Qaeda (Jordan et al., 2004; Bouzis, 2015).

While most of the literature on intelligence and terrorism since 9/11 has focused on the threat from al-Qaeda and other Islamist groups such as ISIL (Pillar, 2014; Bouzis, 2015), some authors look at other terrorist problems. Examples include the British use of intelligence in Northern Ireland (Bamford, 2005), Greek intelligence success in dismantling the 17 November group (Nomikos, 2007), and the lessons to be learned from the Israeli intelligence community’s experience with terrorism (Kahana, 2005; Pedahzur & Perliger, 2007).

Although there continues to be agreement that greater information sharing is needed within the intelligence and counterterrorism communities, there is a growing belief that an equally important problem is that of having too much information. Builta and Heller (2011) write, “Many of today’s problems are rooted in the problem of having too much data, too many diverse stovepipes creating it, and difficulties in scrutinizing the abundance across unique data sets” (p. 4). Studies focusing on the importance of “big data” for counterterrorism intelligence include Skillicorn and Vats (2007) and Leetaru (2015).

Scholars studying the intersection of intelligence and terrorism are quite aware of the importance of producing policy-relevant work. As Arthur Hulnick (2005) writes, “Nothing is more important in the world of intelligence than preventing surprise” (p. 593). But in general, the literature on intelligence and terrorism is more useful for understanding the limitations of intelligence in preventing terrorist attacks than in proposing ways to improve that performance. A few writers, including Hulnick, Khalsa (2004), and Sinai (2007), have examined the question of developing indications and warning (I&W) systems for forecasting terrorist attacks, and more work here could potentially be of great value.

Another area where additional research is needed is in the study of intelligence success against terrorism. Marrin has called for such work, but he notes that research on intelligence success is likely to be difficult, because the information needed is probably classified: “while such a study of successes may be promising, it would also be very difficult to accomplish from outside the intelligence community” (Marrin, 2004, p. 661). Among the few works that do discuss intelligence successes are Betts (2002, 2007), Irons (2008), and Dahl (2013).

Much of this literature focuses on the analysis and collection of information and on how it is disseminated to decision makers and other customers. Although several authors note that other intelligence disciplines such as covert action and counterintelligence are critical in the struggle against terrorism, relatively little work has been done that focuses on those topics. Exceptions include Le Gallo (2005) on covert action, and Wannall (2002), Danis (2007), Shultz and Beitler (2004), and Mobley (2012) on counterintelligence.

The problems inherent in balancing security with civil liberties in democracies have been examined by Bruneau (2008) and Richards (2012), among others. Although a full discussion of this topic is beyond the scope of this essay, the literature in this area has expanded considerably since the revelations by Edward Snowden of the National Security Agency intelligence collections programs.

Scholars such as Arce and Sandler (2007) use the tools of game theory to improve our understanding of how intelligence can be used against terrorism, and more work here could prove very useful.

More broadly, there has been little work attempting to carefully examine the question of whether terrorism presents a truly new problem for intelligence, or whether it simply echoes the challenges seen by earlier generations of analysts and collectors. (Exceptions include Lesser et al. [1999] and Copeland [2001].) A number of scholars and analysts have noted similarities between the two most notable examples of such attacks against America, Pearl Harbor and 9/11; useful examples include Wirtz (2002) and Borch (2003). But more research is needed into the broader theoretical similarities and differences between the problem of surprise attack from terrorism today, and into the challenges posed for intelligence by conventional attack or by other types of surprises. (A notable exception to this gap is Marrin [2004].)

Relatively few detailed case studies have been produced of how intelligence performed in the face of terrorist attacks other than 9/11, likely because information is difficult to obtain. Exceptions include Segell (2005) on the Madrid train bombings and Dahl (2005) on the 1983 Marine Barracks bombing in Lebanon. Most studies of the American intelligence community focus on the CIA and (to a lesser degree) the FBI. Considerably less work has been done on the many other agencies that make up U.S. intelligence. Exceptions include Jones (2006), Logan (2010), and Steiner (2015) on the intelligence activities of the Department of Homeland Security.

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