The Long History of Violent Extremism

While the annals of the ancient world are full of violence, the social context and ideological justifications that survive are often incomplete. One of the earliest examples of a social trend that resembles extremism as we know it today can be found in the Roman war on Carthage in the second century BCE, which has been described by Yale scholar Ben Kiernan as “the first genocide.”

Carthage, located in modern-day Tunisia, was the capital of one of ancient Rome’s regional competitors. After three devastating wars, Rome captured the city and disarmed the citizenry. Yet some Roman politicians argued that the threat posed by Carthage was so dire that it could not be addressed simply by conquest.

A Roman senator known as Cato the Elder was famously reported to conclude every speech he gave to the Senate with the phrase “Carthago delenda est” (“Carthage must be destroyed”), no matter what the subject of the speech happened to be. Cato was an early populist-nationalist. He was a paleo-conservative even relative to the standards of the day — militaristic, misogynistic, and racist, comparing the perceived decadence of his contemporaneous society to a mythical golden age of days past. He believed that Carthage represented a threat to the existence of Rome and the purity of its culture. Because of this, victory was not enough: “Carthago delenda est.”

The Third Punic War began with Carthage almost immediately surrendering to Rome and disarming. Unsatisfied with the terms of that surrender, Rome demanded that the Carthaginians abandon the city, which the Senate had already decided to destroy. When the residents refused to leave, Rome launched a siege that ended with Carthage razed to the ground. The decision to continue past the Carthaginian surrender and the rhetoric of Cato frame the destruction of Carthage squarely as a recognizable example of extremism. It is estimated that 150,000 or more died when the city fell.

Carthage is arguably the earliest well-documented historical example of genocide and nationalist violent extremism. There are reports of more ancient events — such as the Trojan War or scriptural accounts that purport to describe Israel’s extermination of the Amelekites. Although these events are not as well documented as the destruction of Carthage, they suggest that a concept of extremism likely existed even earlier in history.

After Carthage, historical records became more robust, and other examples quickly emerged. One identity movement founded during the early first century CE was known as the Zealots. Much has been written about the sect, although some of that scholarship is colored by Christian interpretations of the group.

One of many anti-Roman groups, the Zealots asserted a unique Jewish identity for occupied Judea and condemned both the Roman invaders and the Jews who cooperated in governing under Roman rule. Its founder condemned Jewish collaborators as cowards and appeared to endorse a theocratic government ruled by priests or a priest-king. Adherents also believed in “zeal,” the root of the movement’s name, meaning a militant enforcement of its views through violence. They battled the provisional government in Jerusalem.

A group within or related to the Zealots, the Sicarii, were said to go further, believing “there should be no lordship of man over man, that God is the only ruler” and killing a Jewish high priest in 65 CE for acceding to Roman rule. The Sicarii were known for carrying out assassinations, property destruction, and theft. According to Josephus, a Jewish-born Roman historian, they “mingled themselves among the multitude, and concealed daggers under their garments,” attacking without warning to strike terror in both Roman and Jewish targets. They became known as perpetrators of atrocities. According to Josephus, the Sicarii committed mass suicide rather than surrender to a siege on their mountain redoubt of Masada in 74 CE, although historians have many questions about the veracity of this account.

The Dark and Middle Ages

In 657 CE, the then-young religion of Islam experienced one of its first major schisms with the rebellion of a sect known to its enemies as the Kharijites or Khawarij (from the Arabic word for seceding). Adherents referred to themselves as As-Shurah, or “the sellers,” in reference to a Quranic verse about selling life in the temporal world in exchange for eternal life in paradise.

The Kharijites broke with the Islamic caliphate in a dispute over succession. The movement was concerned with restoring the practice of Islam as they imagined it to have been two generations previously. The caliph of the day, Ali, brutally crushed the Kharijite rebellion and was subsequently assassinated by one of the sect’s adherents.

As with many historical movements, views of the Kharijites are colored by the passage of time and the well-known effect of history being written by the victors. For instance, Irenaeus, one of the Fathers of the Church, was for many years the primary authority on the Gnostic sect of early Christianity. But the discovery of a cache of well-preserved original Gnostic texts in 1945 revealed that his descriptions of the sect were often and significantly inaccurate. Histories of heresy are written by the orthodox victors.

Thus, the Kharijites have become associated with violent extremism thanks to the work of mainstream Islamic historians over many years, but it is not entirely clear how much of its reputation is grounded in reality. Nelly Lahoud, a scholar of political Islam, writes that the notoriety of the Kharijites grew in direct proportion to the fame and status of Ali. Additionally, Muslim scholars have in recent years come to rely on the term as a pejorative to condemn jihadist terrorism, further coloring views of the group.

With that caveat in place, the understanding of the Kharijites as extremists may have some basis. Like the Zealots, the Kharijites are remembered for their zeal, both in their stringent practice of Islam and the use of political violence in its defense. Most accounts agree that they were hardcore fundamentalists looking back to a golden age of Islam, albeit one that had barely passed in their lifetimes. Their commitment was so focused that it was said they could seduce even their enemies to become adherents.

Kharijites were said to evaluate other Muslims for purity and correct belief, killing those who failed to meet their definition of Islam. They were reputed to have brutally killed Muslims who failed the test, along with their families, including women and fetuses cut from the womb. They may have believed that any sin rendered the sinner an apostate from Islam.

The wars between (and within) Christianity and Islam during the Middle Ages are too vast to explore in detail here. But one particularly memorable case of heresy-hunting took place in the 13th century Roman Catholic Church. The Cathars were a Christian religious sect based in the south of France whose beliefs were wildly different from the orthodoxy of Rome. Its practices were also notably different, with unique sacraments and a commitment to living modestly, in contrast to some Catholic clerics of the day.

A succession of popes sent emissaries and messages to urge repentance in increasingly dire terms. Some of these entreaties reportedly met with violent responses. Finally, Pope Innocent III called a crusade, offering the forgiveness of all sins for those who would “tear up the unserviceable roots from the vineyard of the Lord” and calling on Christian men “kindled with the zeal of orthodox faith to avenge just blood — which does not cease to cry out from earth to heaven, until the Lord of Vengeance shall descend from heaven to earth to confound both subverted and subvertors.”

The toll was staggering, resulting in widespread torture and the massacre of likely hundreds of thousands of Cathars until the religion and its supporters had been eradicated. The conflict between the Catholic Church and the Cathars also led directly to the establishment of one of the most horrific institutions in history, the Inquisition.

The New World

Starting in the 16th century, Spanish conquistadors sought to colonize the Americas through a program that may have started as military conquest but soon escalated into racial extremism. They perpetrated the most horrific genocide in human history, resulting in the extermination of whole societies of indigenous peoples in the Americas. The actions of the conquistadors left as many as 70 million dead through a combination of intentional massacres, the effects of enslavement, and the introduction of deadly diseases.

The line between war and extremism is often muddy, but the conquistadors executed their campaign in reprehensible excess and with the support of a legitimizing ideology. Spanish philosopher Juan Ginés de Sepúlveda wrote that the indigenous people of the Americas were “half-men” or “homunculi,” who possessed “barely the vestiges of humanity” and deserved only conquest and enslavement. Later colonizers of the New World and Australia also relied on various ideological justifications for their acts, although these were often a thinly veiled excuse to indulge a cruel and epic greed.

Slavery, broadly, had been a part of warfare and conquest for millennia, as well as being a criminal punishment or a mandated satisfaction of debt in some cultures. Hereditary or chattel slavery — the concept that a slave’s descendants must also be slaves — was less common, but it became a growing force after the 15th century as a series of papal proclamations helped legitimize the practice in conjunction with the colonization of the Americas and the concurrent rise of the African slave trade. During the course of these debates, a variety of conflicting religious views (both Catholic and Protestant) emerged as to whether Indigenous peoples and other nonwhite races could be considered human and whether their enslavement was justified regardless. The institution — and its racialization — grew despite these ambiguities and shifting views.

In the colonial Americas, Virginia passed a law legalizing hereditary slavery, and other colonies soon followed, embedding the practice deeply in the economy and culture of the nascent United States. Disagreements over the morality of slavery slowly grew into a force strong enough to break a nation. The rise of the abolitionist movement in the early nineteenth century and its attacks on the legitimacy of what was called the “peculiar institution” led to the crystallization and codification of extremist proslavery ideologies.

“Can these two distinct races of people now living together as master and servant, be ever separated?” asked the proslavery writer Thomas Roderick Dew. “Can the black be sent back to his African home, or will the day ever arrive when he can be liberated from his thralldom, and mount upwards in the scale of civilization and rights, to an equality with the white?”

In order to preserve slavery, extensive ideological justifications were advanced. Southern intellectuals leapt to the task, citing sources both biblical and “scientific.” They also drew on historical precedent, citing past civilizations that had thrived on the institution (often eliding the distinction between nonhereditary slavery and its hereditary, racialized offshoot).

No one really knows how many slaves were held in captivity in the United States and elsewhere over the duration of the practice. Likely a minimum of 10 million African slaves were trafficked to the Americas, and at the conclusion of the Civil War, nearly 4 million slaves were freed in the United States alone. The total human cost of the African slave trade and the succeeding generations of hereditary slavery certainly run into the tens of millions, one of the gravest shames in the history of humanity and one of extremism’s greatest triumphs.

The Twentieth Century and Beyond

The origins of anti-Semitic extremism, in its religious aspect, can be traced back millennia, but in France and Germany during the late 19th century, it evolved into an ideology that viewed Jewish identity not just as religious but also as racial. Anti-Semitic beliefs took hold with special ferocity in Germany, where decades of war and social upheaval created conditions ideal for the persecution of a minority that could blamed for loss and uncertainty.

A confluence of events, anchored by German nationalism and virulent anti-Semitism, led ultimately to the depredations of the Nazi regime, which killed 6 million Jews and at least 12 million others between 1933 and 1945 through campaigns of genocide, the horrors of concentration camps, programs of mass starvation, and other atrocities outside of the wartime death toll, which added tens of millions more on all sides.

Even in defeat, elements of the poisonous Nazi ideology live on today in hundreds of successor movements around the world that are dedicated not just to German racial purity and nationalism but to a broad spectrum of white supremacist beliefs, from the United States to Greece, Russia to Australia. The influence of Nazism endures today not only among relatively small groups of direct adherents but in broader international and political dynamics, including a host of politically corrosive conspiracists who endlessly recycle anti-Semitic tropes using euphemisms such as “globalist.”

The 20th century was rife with extremism — the anarchist assassination of U.S. President William McKinley in 1901, the Serbian nationalist assassination of Austrian Archduke Franz Ferdinand in 1914 (one of the events that helped trigger World War I), the Stalinist massacres of the 1930s, and the slaughter of as many as a million Tutsis in Rwanda in 1994. There have been many more — too many to describe here.

In the winter of 1979, a series of events rocked the Muslim world, setting the stage for the extremist scourge that dominates most discussion of the topic today — the jihadist movement. Iranian revolutionaries overthrew their nation’s secular government and established an extreme theocracy, setting the stage for the later emergence of the formidable Shia jihadist movement Hezbollah and a host of other Shia sectarian militias. Soon after, in Saudi Arabia, a band of apocalyptic extremists laid siege to the Grand Mosque in Mecca, the holiest site in Islam, in a terrorist attack that left hundreds dead and paralyzed the country for weeks.

Perhaps most fatefully, the Soviet Union invaded Afghanistan at the end of 1979, triggering a decades-long sequence of events that has shaped much of the 21st century. In response to the invasion of a Muslim country, hundreds and then thousands of foreign fighters made their way to Afghanistan to fight the Soviets as mujahideen, warriors in defense of their coreligionists. In the United States, the mujahideen were seen at first as freedom fighters. Their leaders were invited to the United States to meet with American politicians. They received overt praise from the State Department and covert support from the Central Intelligence Agency. The head of the foreign fighter battalions, Abdullah Azzam, traveled to the United States repeatedly, openly recruiting American Muslims to join the battle.

As the nearly decade-long war began to wind down with the Soviets in retreat, veterans of the foreign fighter movement decided their work was not finished. In 1988, Osama bin Laden organized a small group of Afghanistan veterans into al Qaeda, an organization dedicated to reshaping the Muslim world. Al Qaeda began as a small and secretive cabal lending aid to Muslim terrorist and insurgent groups around the globe.

During the 1990s, Serbian nationalist extremists carried out genocidal attacks that resulted in thousands of Bosnian Muslims being killed, displaced, and placed in concentration camps. These extremist attacks provoked an extremist response. At least hundreds of foreign jihadist extremists — many trained by or affiliated with al Qaeda — joined the Muslim defense effort, alongside hundreds more jihadists of Bosnian origin. Although an uneasy peace was brokered between the warring sides in 1995, extremists from both camps continue to plague the region in significant numbers.

Al Qaeda sought to overthrow corrupt Middle Eastern regimes and replace them with Sunni theocracies. Because bin Laden and his cohort believed the movement could not accomplish this without depriving Arab rulers of American financial and military support, al Qaeda began to direct terrorist attacks against the United States, first by supporting loosely connected extremist groups (as in the 1993 World Trade Center bombing) and later with its own highly professional operations (such as the 1998 synchronized bombings of U.S. embassies in East Africa).

On September 11, 2001, al Qaeda carried out the most devastating terrorist attack in history, hijacking four airplanes and successfully crashing three of them into the World Trade Center towers and the Pentagon. In response, the United States launched a “War on Terror” that continues to this day. The resulting social and political upheaval has too often placed Muslims at the center of public debate and policy regarding extremism.

In the wake of the U.S. invasion of Afghanistan, where al Qaeda was based, the organization spread out geographically, first under a relatively centralized affiliate model. But over time, the cohesion of the organization was tested by internal politics and external pressures. The affiliates increasingly waged insurgencies in their local realms and neglected their original focus on the United States and a global jihad.

The most important fracture took place in Iraq, home to the first official al Qaeda affiliate, which formed in response to the 2003 U.S. invasion of that country. Al Qaeda in Iraq was founded by Abu Musab al-Zarqawi, a Jordanian jihadist whose views were even more extreme than those of bin Laden. Al Qaeda in Iraq almost immediately came into conflict with its parent group. After a decade fighting U.S. and Iraqi forces with varying degrees of success, it went through a series of reorganizations and finally established itself as an entity completely independent of al Qaeda, known as the Islamic State or ISIS.

The Islamic State represented an evolution of al Qaeda’s ideology. It was more violent and against a much wider variety of targets. Where al Qaeda tried (selectively and with mixed results) to minimize Sunni Muslim casualties in its attacks, Islamic State massacred Sunnis by the hundreds. Where al Qaeda put less emphasis on the divide between the Sunni and Shia sects of Islam, Islamic State calculated its attacks to widen it, making Shia Muslims its archenemy, above all others, even the hated Americans and Jews.

As jihadist movements proliferated and diversified, the issue of understanding extremism became more contentious, contested, and confusing. In Syria, Bashar al-Assad’s regime brutally slaughters civilians by the thousands and justifies the carnage by claiming it is fighting extremists. Within the Syrian opposition itself, fractious infighting revolves around the question of which rebels are the noble opposition and which are jihadist extremists. And even the true jihadists in Syria are splintered into more and less radical camps, constantly accusing each other of extremism while exonerating themselves. Jihadist rebels define their extremism against each other and against Islamic State, which is a deadly enemy to most of them, despite great similarities in their ideologies.

In Myanmar, Buddhists have been swept up in this cycle, practicing discrimination or worse against members of its Muslim Rohingya minority for decades before opening a genocidal campaign of ethnic cleansing in the late 2010s. Like anti-Muslim extremists in other countries, radical Buddhist monk Ashin Wirathu says his victims are the real extremists. “You can be full of kindness and love, but you cannot sleep next to a mad dog,” Wirathu has said, seeking to reconcile traditional Buddhist teaching with his campaign of hate and fearmongering.

The alt-right movement that rose up in the United States during the 2010s predicated bigotry against Muslims on the assertion that Islam itself is fundamentally extremist, and the high frequency of terrorist attacks by Islamic State throws fuel on that fire. In the view of the alt-right, every Muslim is a potential terrorist and an active cultural infiltrator seeking to establish Islamic religious rule in the United States. The alt-right has been succeeded by a more sweeping and equally virulent anti-immigrant extremism that targets ever wider groups of people. Many hardcore anti-immigrant activists would deny that they are extremists, and some claim that immigrants are the real extremists.

One of the most painful and contentious examples is the conflict between Israel and people in the occupied Palestinian territories. When Hamas committed a horrific and brutal mass terrorist attack on October 7, 2023, the Israeli government responded with devastating force that left tens of thousands of Palestinian civilians dead and hundreds of thousands stranded in an ongoing humanitarian crisis, leading to an accusation of genocide before the International Court of Justice. Many people around the world have irreconcilable differences in their views about this conflict and the social and political landscape that preceded it.

If there is any lesson to learn from these modern and historical examples, it is this: defining extremism is not a casual matter. “I know it when I see it” is not an acceptable standard when so many lives are at stake. It is not enough for a world where the course of history has repeatedly changed as a result of extremist violence.

J. M. Berger is a Senior Research Fellow for the Center on Terrorism, Extremism, and Counterterrorism (CTEC) at the Middlebury Institute of International Studies, co-author (with Jessica Stern) of “ISIS: The State of Terror” and the author of “Jihad Joe: Americans Who Go to War in the Name of Islam” and “Extremism,” from which this article is excerpted. The article has been edited to reflect events since the publication of the book in 2018.