Precursors

David C. Rapoport’s approach to the study of terrorism appeared in the 1970s. It offered unique insights into the religious implications of terrorist campaigns. Whereas the first generation of terrorism scholars—Walter Lacquer, Alex Schmid, Martha Crenshaw, and others—largely approached the subject as a purely political phenomenon, Rapoport argued that religion was a vital component of terrorist violence. In this, his was a voice in the wilderness. Remarkably, even in the wake of the 1979 Iranian Revolution, the rise of al-Qaeda, and the War on Terror, many of the most influential scholars in the field continued to argue that terrorism was ineluctably political and that the leaders of religiously motivated terrorist groups were undoubtedly clever political operators who manipulated religion for political ends (Hoffman, 2018).

Rapoport’s unique approach, which gave birth to wave theory, began with a course at the University of California, Los Angeles, that focused on the Hebrew Bible and resulted in an early article, “Moses, Charisma, and Covenant” (Rapoport, 1979).¹ Although the article is largely forgotten today, it challenged political scientists to take the Bible seriously as a source for political action. It was followed by his seminal 1980s articles, which focused on terrorism in the ancient world and from which many of the tropes of modern terrorism can be traced.

What followed laid the groundwork for the study of religiously motivated terrorism and, in the process, inspired a handful of future terrorism scholars to pursue the study of religion and terrorist violence.² Rapoport’s trilogy of articles comprising “Fear and Trembling: Terrorism in Three Religious Traditions” (1984), “Terror and the Messiah: An Ancient Experience and Some Modern Parallels” (1982), and “Messianic Sanctions for Terror” (1988) marks the beginning of the contemporary study of religiously motivated terrorism. All three brought home the vital importance of religious zeal in maintaining a prolonged campaign of terrorism. They stressed the primacy of sacred texts in the ancient world as the key factor in motivating and sustaining terrorist violence. Moreover, they conclusively demonstrated the fact that terrorism, heretofore believed to be a purely modern phenomenon, was a timeless reaction to existential threats that were beyond the faithful’s capacity to survive without compromising or abandoning their faith. Salvation must therefore be metahistorical in nature. Only divine intervention could save the faithful while punishing both the guilty and those whose inaction or simple indifference was deemed as tacit support for the oppressors.³ In a terrorist campaign, there are no innocents and no bystanders.

Of the three articles, “Fear and Trembling” (1984) was both groundbreaking and the true precursor to the four waves. It was the first published article to explore on a comparative basis religious terrorism that, by including the Indian Thugs, demonstrated the global impact of terrorism beyond the three Abrahamic traditions: Judaism, Christianity, and Islam. The three articles (Rapaport, 1982, 1984, 1988) were published at a time when terrorism was being downplayed by academics and the U.S. government alike, drying up funding for terrorism research.⁴ In “Fear and Trembling,” Rapoport detailed the similarities in tactics, weapons, and communications—all tied to extant technologies—which he views as the threads that bind movements of different times, religions, and geographic regions together. In his words:

The cases [the Sicarri, the Assassins, and the Thugs] are inherently interesting and peculiarly instructive. Each group was much more durable and much more destructive than any modern one has been; operating on an international stage, they had great social effects too. Yet the noose, the dagger, and the sword were the principal weapons they employed, travel was by horse or foot, and the most effective means of communication was by word of mouth. Although a relatively simple and common technology prevailed, each example displayed strikingly different characteristics. The critical variable, therefore, cannot be technology: rather, the purpose and organization of particular groups and the vulnerabilities of particular societies to them are decisive factors. Although the point may be more easily seen in these cases, it must be relevant, I shall argue, in our world too.

(Rapoport, 1984, p. 659)

This introduction, with its emphasis on technology and the signature weapons of each group, begins to lay the groundwork for what would become wave theory. Its conclusion explicitly states the cyclical character of terrorism, which is the foundation of wave theory:

This conclusion should shape our treatment of the dynamics of modern terrorism. There is no authoritative history of modern terrorism that traces its development from its inception more than a century ago. When that history is written, the cyclical character of modern terror will be conspicuous, and those cycles will be related not so much to technological changes as to significant political watersheds, which excited the hopes of potential terrorists and increased the vulnerability of society to their claims. The upsurge in the 1960s, for example, would be related to Vietnam just as the activities immediately after World War II would appear as an aspect of the decline in the legitimacy of Western colonial empires. Since doctrine, rather than technology, is the ultimate source of terror, the analysis of modern forms must begin with the French, rather than the Industrial Revolution.

(Rapoport, 1984, p. 672)

The publication of these articles in the 1970s and 1980s, alongside a separate study on the particular affinity of messianic and millenarian movements with terrorist violence, would culminate a quarter-century later in Rapoport’s wave theory (Rapoport, 1987, pp. 72–88).⁵

The waves idea ultimately came together in the wake of 9/11 in David C. Rapoport’s article “The Four Waves of Rebel Terror and September 11” (Rapoport, 2002). In the opening paragraphs of that article, Rapoport stated:

September 11, 2001 is the most destructive day in the long bloody history of rebel terrorism. The casualties and the economic damage were unprecedented. It could be the most important day too. President Bush declared a “war” to eliminate terror, galvanizing a response that could reshape the international world. Exactly 100 years ago, we heard a similar appeal. An Anarchist assassinated President William McKinley in September 1901, moving the new president Theodore Roosevelt to summon a worldwide crusade to exterminate terrorism everywhere. Will we succeed this time? No one knows, but even a brief acquaintance with the history of terrorism should make us more sensitive to the difficulties ahead. To this end, I will briefly describe rebel terrorism in the last 135 years to show how deeply implanted it has become in modern culture. The discussion is divided into two sections. The first describes the four waves of modern terror, and the other focuses on the international ingredients in each. I will discuss the political events triggering each wave, but lack space to enumerate the great and persistent domestic impacts.

(Rapoport, 2002)

The Four Waves of Modern Terrorism

Appraisals of Wave Theory

Wave theory has come to be widely accepted in the field as a useful historical model. The insights it provides into both the international character of terrorism and its transnational commonalities and modalities are undeniable. That said, every theory must be a constant work in progress if it is to have continuing utility in a rapidly evolving field. Some of the difficulties with wave theory have already been pointed out in this article. Problems of classification, as with the Palestine Liberation Organization (PLO), are not of great import. The generational nature of wave theory is one of its major strengths, although the religious wave seems to defy the single-generation lifespan allotted to each wave. Therefore, it would be useful to examine some of the difficulties and objections that have been expressed about wave theory.

We will begin with a reexamination of the second wave and a consideration of what might be termed ethnonationalist violence. This will be followed with a consideration of the literature of the four waves. Terrorism, Identity and Legitimacy: The Four Waves Theory and Political Violence, an anthology edited by Jean Rosenfeld, is a Festschrift that is well disposed to wave theory (Rosenfeld, 2011). This is followed by a very different view in a critical article, “The Four Horsemen of Terrorism—It’s Not Waves, It’s Strains,” (Parker & Sitter, 2016, pp. 197–216), which was accompanied by a rebuttal piece from David C. Rapoport and commentary from Charles Townsend and Jeffrey Kaplan (Kaplan, 2016a, pp. 228–235; Rapoport, 2016a, pp. 217–224; Townsend, 2016, pp. 225–227).

The second wave focuses on anticolonialist violence. As we have seen, the explosion of newly independent and newly established nations in the runup to the early 1960s is a testament to the global triumph of nationalism. Whereas nationalist aspirations were repressed in Northern Ireland, the Turkish zone in Cyprus, former Yugoslavia, and throughout the Soviet empire, terrorist groups survived and flourished when most second-wave groups were matters of historic debate. Ethnic terror marked the Yugoslavian wars in the 1990s, with Serbia and Croatia leading the way in the application and historic importance of ethnically based terror. Croatia’s Nazi past attracted young National Socialists from Germany and Scandinavia to fight on the Croatian side during the conflict.³⁴ Of far greater current concern is terrorism in the former Soviet Union (FSU), with Chechen terror constituting a global threat.³⁵

Rapoport was certainly aware of the importance of ethnic violence and the emergence of ethnonationalist terrorism. He wrote important articles on the topic, both from historical and contemporary perspectives (Rapoport, 1996, pp. 258–285). Much of this work, however, was not fully reflected in his discussion of the second wave.

There are numerous examples of ethnoterrorism to consider, but it is clear that there are some questions about the efficacy of wave theory to be derived from the topic. Rather than delve into so vast a corpus, it would be useful to rethink the problem in another way. If, as Rapoport suggests, the fourth wave will recede by 2019, will the fifth wave focus on ethnonationalist terror? This possibility will be considered at greater length in the discussion of speculations about the emergence of a fifth wave of modern terrorism.

Leonard Weinberg suggests the possibility that the fourth wave will end as scheduled, while Eubank and Weinberg’s “An End to the Fourth Wave of Terrorism?” is a brief account of a monograph that would appear two years later as the broader An End to Terrorism? (Weinberg, 2012; Weinberg & Eubank, 2010). The article argues that the radical right does not easily fit into any of the four waves (Weinberg & Eubank, 2010, p. 596). Historically, however, religiosity has been deep in the heart of the radical right, be it every stage of the Ku Klux Klan, the Turkish Grey Wolves, Christian Identity, or any of the many varieties of postwar National Socialism.³⁶ Using a statistical approach, the rest of the article makes the cautious argument that:

What can be suggested is that some evidence indicates the Fourth Wave of modern terrorism may be on a downward trajectory … The Egyptian groups Jihad and al-Gamma al-Islamyya, responsible for major terrorist attacks, have declared their abandonment of violence. Next, domestic and international authorities have strengthened their ability to monitor, detect, and prevent terrorist attacks. There is evidence that Al Qaeda and its affiliates have induced disaffection among the very people they want to take up the cause of jihad. Public opinion in the Muslim world may be shifting, a result of terrorists staging indiscriminate or insufficiently discriminating attacks on fellow Muslims.

(Weinberg & Eubank, 2010, p. 600)

The rise of the Islamic State, the resultant flood of refugees into Western Europe, and the numbing series of high-casualty terrorist attacks from 2013 to the present makes this appear to be somewhat overly optimistic. The case is further complicated by the rise of Islamist violence toward Jews in a developing fusion between radical Islam and the radical right. France is at the epicenter of this wave of religious terrorism, but it has impacted many places in Western Europe (Celso, 2020; Easat-Daas, 2020, pp. 197–248; Michael, 2006).

Weinberg and Eubank’s article was clearly written in support of the generational aspect of wave theory, but it only muddles the case. The first phase of the Ku Klux Klan, for example, began during the American Reconstruction period after the Civil War in the 1870s, yet the organization was religious in concept and symbolism, and that religiosity would characterize the group throughout its history. Even its sacred book—ironic, given the current Islamophobic climate—is called The Kloran!³⁷

David C. Rapoport is aware of the difficulty of classifying the radical right and other forms of popular violence in the context of wave theory. In 2008, he published a fascinating article (Rapoport, 2008a) that sweeps through American history and finds a history of mob violence. That article, “Before the Bombs There Were the Mobs: American Experiences with Terror” is a fascinating subtext to wave theory.

Leonard Weinberg would examine the problem of what might follow the fourth wave in The End of Terrorism? (2012). After suggesting and dismissing a number of fifth-wave suspects, he again expresses admirable if possibly misplaced optimism in stating that perhaps terrorism will disappear altogether; or less grandly, that it will return to the margins of political violence from whence it came in the 20th century (Weinberg, 2012, pp. 125–127).

Finally, as we have noted, Terrorism and Political Violence in 2016 published a forum on wave theory in response to Tom Parker and Nick Sitter’s criticism of wave theory, “The Four Horsemen of Terrorism—It’s Not Waves, It’s Strains” (2016). Parker and Sitter begin badly for most terrorism scholars by proposing a disease model, viewing terrorism as an infection whose unfortunate sufferers are caught up in a disease vector or strain. They are ultimately the victims of an infection that can be traced to a putative patient zero, making terrorism a particularly virulent malady much akin to a zombie outbreak aka The Walking Dead. Medicalizing terrorism is a bane for terrorism scholars, but it makes a kind of sense given Parker’s background: “Tom Parker was formerly Policy Director for Terrorism, Counter-Terrorism, and Human Rights at Amnesty International USA, and Adviser on Human Rights and Counter-Terrorism to the United Nations Counter-Terrorism Implementation Task Force (CTITF)” (Parker & Sitter, 2016, p. 197). It is far easier to appeal for humane treatment of terrorists in the age of ISIS with a medical appeal than it would be with a national security approach.

That said, Parker and Sitter’s view of terrorism is strikingly pessimistic, and indeed, apocalyptic. The title of the piece reflects an effort throughout the article to use the Four Horsemen of the Apocalypse as a metaphor for global terrorism. The authors state:

The four strains we have identified all date from the same period, and although they have mostly developed separately since, they do occasionally combine and mutate. These four strains—these four horsemen of terrorism—are Nationalism, Socialism, Religious Extremism, and Social Exclusion. Using Boaz Ganor’s definition of terrorism—“the intentional use of or threat to use violence against civilians or against civilian targets, in order to attain political aims”—as our criteria, we have compared both theories against the historical record to determine which ultimately offers the greater theoretical leverage over recorded events.

(Parker & Sitter, 2016, p. 199)

While the strains and horsemen are not, in essence, significantly different from Rapoport’s waves, the article does make some valid points about the difficulty of classifying some groups in particular waves. The Egyptian Muslim Brotherhood (Ikkwan), for example, was born in 1929 in the second or nationalist wave. Yet the Ikkwan’s members were not primarily nationalist in orientation. Rather, they were religious and from the beginning saw national independence in profoundly ambivalent terms, stating that “political independence was worthless unless accompanied by intellectual, social, and cultural independence” (Mitchell, 1993, p. 230). Further complicating the issue is a factor that is often overlooked, and completely missed by Parker and Sitter; the Brotherhood was a complex political organization that only occasionally indulged in terrorism. Waves or strains, the theory of terrorist violence does not address anything but terrorism and thus needs to focus primarily on that, rather than deviant politics. Rapoport’s wave theory does exactly this. Parker’s “The Four Horsemen” does not. This factor alone would support the utility of Rapoport’s wave theory.

But there is more. As Robert Townsend states:

One doubtful aspect of their proposal might be that the idea of “strains,” especially when accompanied by a search for a “patient zero” for each strain, seems to echo the notion of terrorism as a kind of disease—an idea that seems to belong to an earlier epoch in the study of terrorism. But whether or not one chooses to call them “strains,” chains, or indeed “horsemen,” it is clearly the case that there are a limited number of key objectives that can mobilise activists prepared to use violence. Parker and Sitter’s article is designed to adjust Rapoport’s four categories along with his metaphor. Do their four “horsemen = strains = chains” cover the spectrum of terrorist motivation better than his Four Waves? Essentially, by fusing two of Rapoport’s categories, the Old and New Lefts, they create a vacant seat for their fourth horseman. (Is it unfair to suspect that they stick to four categories to tally with the apocalyptic metaphor?) … As ever, framing is key here, and the “four horsemen” are in essence a re-framing of Rapoport’s categories. Whether one thinks Parker and Sitter’s frame works better than Rapoport’s depends on such issues as whether one places the Ku Klux Klan in the terrorist mainstream as they do, or outside it as Rapoport does. Both make sense. In the end, it may not really be an issue of choosing between waves and strains; the analytical frames of Rapoport and Parker and Sitter possess convincing explanatory and ordering power. The kinetic effect of the wave and the continuity of the strain, both correspond to a useful degree with messy reality. Maybe there is here a case for defying Fowler and deliberately mixing metaphors—producing a wavy strain, perhaps? What we do not need is to add a third metaphor: the horsemen would be better riding off into the sunset.

(Townsend, 2016, pp. 226–227)

The Fifth Wave

The 40-year generational cycle of religious terrorism came and went in 2019 without a significant waning of terrorist violence—indeed, the rise and fall of the Islamic State from 2004 to 2017 and its continued vitality as a terrorist network and the return to power of the Taliban in Afghanistan in 2021 would argue that there is plenty of life left in the wave of religious terrorism (“Timeline: The Rise, Spread, and Fall of the Islamic State,” 2019). That al-Qaeda survived the death of Osama Bin Laden in 2011 is further evidence that religion remains a powerful motivator for terrorist violence.

That said, the quest for a fifth wave goes on. Jeffrey Kaplan and others have suggested that the next wave will be focused on ethnicity, which he and Christopher Costa have dubbed the “New Tribalism” (Kaplan & Costa, 2014). Others, particularly after the dramatic demise of the Trump presidency, agree with Weinberg et al. that the radical right will constitute the next wave. Indeed, David Rapoport himself, in his forthcoming monograph (as of this writing in 2021) weighs in with his belief that the radical right will indeed constitute the next wave of terrorism (Rapoport, forthcoming). A closer look at both theories is thus in order.

Jeffrey Kaplan’s speculations on a possible fifth wave focus almost entirely on ethnic terrorism, which as Alex Schmid points out in his brilliant The Routledge Handbook of Terrorism Research, is not a crowded field (Schmid, 2011, pp. 234–236).³⁸ Kaplan’s fifth-wave monograph followed several journal articles to make the case that the next wave of terrorism would be ethnic in character. All focused primarily on Africa, and all described unique aspects of contemporary ethnic and ethnonational terrorism. Kaplan offers a checklist of the characteristics of fifth-wave ethnoterrorism:

An ideal case of fifth-wave terrorism would have all of the following characteristics:

(Kaplan, 2007, p. 548)

The checklist outlined an ideal case of millennialist ethnic terror, and well describes cases ranging from Serbia in the Balkan wars to the Lord’s Resistance Army and Boko Haram in Africa. Anthony Celso later expanded the theory to include the Middle East, with special emphasis on the Islmic State (also known as Daesh or ISIS) and al-Qaeda (Celso, 2015). Kaplan’s fifth-wave theory has become fashionable among younger scholars, but it fails to be a global model covering both the Western and developing world. The fifth-wave material led, however, to the New Tribalism, an intricate model that, through Colonel Christopher Costa, has made its way into the American national security and military command structure as a route to a deeper understanding of global terrorist movements, as well as into the process of radicalization and mobilization.³⁹

Following the 2021 insurrection in Washington that sought to prevent Congress from certifying the 2020 U.S. Presidential election, the far right became the ubiquitous choice as the source of the fifth wave of global terrorism. At the crest of this scholarly wave will surely be the concluding chapter to David Rapoport’s The History and Future of Terrorism which posits the far right as the next wave (Rapoport, forthcoming).

The chapter, somewhat surprisingly, does not make explicit reference to the key integers of wave theory, but it does include all the requisite ingredients. For Rapoport, the wave is a response in particular to immigration in Western Europe and the United States. Immigration fears have given new life to right-wing populist parties, some of which have explicitly neo-Nazi roots but which, with a change of leadership and tone, have moved increasingly into the mainstream. These parties have gained seats in national and European parliamentary elections, moving anti-immigrant rhetoric from the margins into the mainstream. Some, as in Trump’s unlikely election in 2016 and, beyond the EU, in parties like the Bharatiya Janata Party (BJP) in India, have actually formed governments and taken power.

The greatest impact of the populist wave has been in Eastern and Central Europe, but the Western states have been impacted as well, often in direct proportion to the number of immigrants who have entered the country in recent years. The rise of the Sweden Democrats in Sweden and of the AfD (Alternativ für Deutschland) in Germany are prime examples. Parliamentary politics is of course not a form of terrorism, but it has two significant impacts on domestic terrorism. First, terrorist groups grow and thrive with the perception that they are supported, at least tacitly, by the national government or government leaders. Second, the availability of a target population, suitably demonized and poorly protected, offers both a rallying cry and a call to action to terrorist groups. Islamophobia serves this role for Rapoport’s view of the fifth wave.

Legislation too plays a role, as it again demonstrates the mainstream view that there is an enemy within the community that needs to be dealt with. The antihijab legislation adopted by several European states serves this function, and the proposed “antiseparatism” legislation in France goes much further (Bourget, 2019). The wave is also greatly facilitated by foreign support, which has been provided in abundance by Vladimir Putin’s Russia, and briefly and on a far lesser scale by Trump’s America (Butt & Byman, 2020).

In the United States, Trump’s 2016 ban on Muslim immigrants served this function. However, he went much further in 2020 as well as in January 2021. In 2020, sensing the election was being lost (due, as much as to anything, to his flailing and increasingly bizarre handling of the coronavirus pandemic), during a presidential debate with Joe Biden he called for the Proud Boys, a Trumpist-oriented militia group, to “stand by and stand ready.” On January 6, 2021, he called for a march on Washington to stop the U.S. Congress from certifying that Joe Biden had indeed won the election. A portion of the mob attacked the Congress, resulting in over 400 arrests and, it is a safe bet, an array of charges that will be filed against Trump, his son Donald Trump Jr., and his attorney Rudy Giuliani (on this bizarre tale, see Kaplan, 2021).

January 6, however, was largely a mob action that terrorist actors like the Proud Boys and the Three Percenters, tried, with some success, to direct. But it was not what might be called the triggering incident that had catalyzed each previous wave. That, Rapoport suggests (though does not really explicitly say) was the 2011 attack in Utøya, Norway, by Anders Behring Breivik (Borchgrevink, 2013).

Breivik’s attack was on a youth group affiliated with a political party and was carried out at a resort island. It was immensely influential among would-be right-wing terrorists and presaged a number of armed attacks around the world. But subsequent attacks by the far right would take on a different character.

Far-right attacks in recent years have focused largely on places of worship, black churches, mosques, and synagogues, or gathering places like public malls. For example, in 2015 Dylann Roof opened fire in a church in Charleston, South Carolina, killing nine people (Zapotosky, 2017). In 2018, Robert Gregory Bowers attacked the Tree of Life Synagogue in Pittsburgh, Pennsylvania, killing 11 (Kissileff & Lidji, 2020). And in 2019, in perhaps the most influential of these attacks, Brenton Tarrant livecast his attack on a New Zealand mosque, in which he killed 51 people. Beyond the scale of the carnage, what made the event a touchstone for the far right was Tarrant’s manifesto, “The Great Replacement,” which has become as ubiquitous in the radical right of today as were David Lane’s 14 words (“We must secure the existence of our people and a future for white children”) a generation ago (Ware, 2020; on Lane’s 14 words, Gardell, 2003). These attacks show no sign of abating, giving some credence to Rapoport’s belief that the far right will eventually prove to be the source of the fifth wave of modern terrorism.

Conclusion

For good reason, David C. Rapoport’s four waves of terrorism theory has become increasingly ubiquitous in the academic study of terrorism. Whereas terrorism in the ancient world was religious in nature and focused on specific locales, the emergence of modern communications technology, from the printed page to the encrypted Internet message, has made terrorism transnational in scope. It is no longer centered on a particular people, a narrow localistic set of religiopolitical circumstances, or even a particular language.

No academic theory is able to capture the full scope of any issue in the social sciences. There remain cases where a terrorist group defies easy classification and where groups outlive their wave and are able to adapt to the changed circumstances of the world around them. These, however, are the exceptions, and they serve to prove the rule. Wave theory’s ability to grow and adapt demonstrates the organic nature of the idea, as well as its academic appeal. It will be a cornerstone in the academic study of terrorism for some time to come.