Some kinds of war produce a snowball effect: war destroys the infrastructure of civilization and with it the livelihood of the civilian population, and the survivors swell the ranks of the army. Something like this happened during the collapse of Bronze Age civilization around 1200 B.C., and during Europe’s Thirty Years’ War. It may have happened, too, when the collapse of the Byzantine and Persian empires in late antiquity began the great wars of Islam, which lasted with brief respites from its first wave of jihad in the early 7th century to the death of Tamerlane on the frontier of China in 1405.

Although the Muslim world has decayed into a geopolitical backwater, jihad remains a threat to Western civilization, though opinions differ about the extent of the threat. If jihad is the expression of an ideology, it could be thwarted by changing (exactly how is another question) the ideology. But if jihad is the consequence of economic and demographic dislocation, it will almost certainly continue to afflict the world’s 1.8 billion Muslims, most of whom live in conditions of economic backwardness and political instability. In this case jihad cannot be extinguished, but only contained.

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From its emergence in the 7th century, Islam’s origins remain wrapped in obscurity. We know much less about the Muslim conquests than we do about many earlier events in the Bible. For example, roughly 3,300 years ago in the Jezreel Valley, Hebrew foot soldiers led by the military commander Barak routed a chariot army under the Syrian general Sisera. Barak chose his ground well, drawing the Syrian chariots close to the muddy soil of the overflowing Kishon River, where the infantry had the advantage. In their Battles of the Bible (1997), Chaim Herzog and General Mordechai Gichon show that the account of the battle in the Song of Deborah (Judges 5) depicts the geography of the historical battleground with remarkable accuracy.

We know more about this ancient battle than about any engagement in the war of conquest from A.D. 620 and 635 that extended Islam’s reach all the way from the Pillars of Hercules to Persia. Islam exploded from the Arabian Peninsula into mastery over half the world in a few decades, yet we know little about how it happened. Yehuda Nevo and Judith Koren observed in Crossroads to Islam (2003) that accounts of this vast conquest were written a century or more after the events, and repeat a mythic formulation from which details are absent. They surmise that former Arab auxiliaries of the (Christian) Byzantine empire assumed control of large swaths of Persian and Byzantine territory emptied out by plague and other disasters.

Nor for that matter do we know whether a man resembling the Muhammad depicted by later Islamic sources ever lived in 7th-century Arabia, or whether the normative Koranic text we have today was recited by this Muhammad, or cobbled together by Muslim rulers two centuries later. For the Islamic world, to question the Koran’s divine provenance is the theological equivalent of denying, in Christendom, the divinity of Jesus.

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In Did Muhammad Exist?: An Inquiry into Islam’s Obscure Origins (2012), Robert Spencer reviewed scholarly objections to the standard account, and argued that the Koran itself was redacted in the 9th century as an apology for the new political order. He cited in particular the work of “revisionist scholars” such as Patricia Crone (1945–2015), John Wansbrough (1928–2002), and the pseudonymous “Christoph Luxenberg.” This unknown writer proposed in a 2000 monograph that the Koran had adapted large sections of the Syriac Christian liturgy, such that reading parts of it in Syriac clarified otherwise incomprehensible passages (he reads, for example, a heavenly reward of 72 “raisins” instead of “virgins”). Alternative Koranic texts unearthed in Yemen seem to refute the Muslim claim that the Archangel Gabriel dictated to Muhammad.

Numerous scholars pointed to textual evidence of the Koran’s multiple authorship and evolution. In a 1999 essay in the Atlantic, Toby Lester argued, “Thus far confined to scholarly argument, this sort of thinking can be nonetheless very powerful and—as the histories of the Renaissance and the Reformation demonstrate—can lead to major social change. The Koran, after all, is currently the world’s most ideologically influential text.”

Hopes that textual criticism would support a Muslim Reformation were also raised by a project at Ankara University to re-examine the Hadith—the narrative of Muhammad’s words and deeds as reported by his companions. Robert Pigott, the BBC’s religion correspondent, wrote in early February 2008 that the Hadith revision would “fashion a new Islam,” while Newsweek entitled its June 8, 2008, cover story, “A New Face of Islam.” The project disappeared and was forgotten, along with the predictions of an Islamic reformation.

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Investigation into the foundations of Islam atrophied as hopes surged for a political revival in the Muslim world. During the so-called “Arab Spring” of 2011-12, the notion of Islamic democracy became for a short while the opium of the elites. The short-lived Muslim Brotherhood government in Egypt during 2012-13 raised hopes both in the Obama Administration and in the neo-conservative wing of the Republican Party that democracy and Islamism might find a happy union. The overthrow of Morsi by the Egyptian military as the country stood at the brink of starvation, the endless civil war in Syria, the collapse of Libya, the permanent war in Afghanistan and, most of all, Turkey’s reversion to strong-man rule, discredited this illusion. At the end of all the slaughter, the Islamic world remains incurious about Koranic criticism, immured in an ideology that rejects self-examination. Meanwhile scholarly examination of Islam and its consequences fell victim to political polarization. President Obama’s declaration before the United Nations General Assembly that “[t]he future must not belong to those who slander the prophet of Islam” amounted to a public threat by the president of the United States against prospective critics of the Koran.

Political correctness has made “Islamophobe” the functional equivalent of “racist,” and few academics will risk their careers and, in some cases, their necks. It takes courage to broach the subject. Robert Spencer, the founder of the Jihad Watch website, is nothing if not courageous. He has written a series of popular books on Islam, including one entitled Confessions of an Islamophobe (2017). The present volume, The History of Jihad from Muhammad to ISIS, is his summa.

William Polk’s Crusade and Jihad, by contrast, blames injured Muslim sensibilities on the depredations of the imperialist “Global North.” Polk writes apologetics rather than history. He claims, for example, that Islam never engaged in forced conversions: “Over the centuries, many Christians and Jews converted to Islam. That Islam forcibly converted them is a myth; actually, the Islamic states preferred that the conquered peoples remain non-Muslim because that status required them to pay an extra tax in lieu of military service.” Spencer, however, quotes a dozen Muslim historians relating conversions at sword point. A former Harvard professor and diplomat, Polk mostly avoids citing Muslim chroniclers, who often boasted about the extent of their side’s atrocities.

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Of all the Muslim conquests, indeed of all the disasters of history, the costliest in terms of human life was that of the 14th-century marauder Timur (Tamerlane). J.J. Saunder in his History of the Mongol Conquests (1971) estimates that the self-styled “Sword of Islam” killed 17 million people, or 5% of the world population, the equivalent of 340 million people today. (Hitler, Stalin, and Mao each exceeded Timur in absolute numbers of the slaughtered, but Timur retains the record for the proportion of population.) Tamerlane’s invasion of India in 1398 was a gusher of blood, including as victims enormous numbers of Muslims, for example the inhabitants of the Tughlaq Sultanate of Delhi, as Spencer reports. Timur’s autobiography claims, among other things, that “in the course of one hour the heads of 10,000 infidels were cut off” and “the sword of Islam was washed in the blood of the infidels” at a single Rajput fortress. At Delhi, Tamerlane wrote, “I proclaimed throughout the camp that every man who had infidel prisoners should put them to death…. One hundred thousand infidels, impious idolaters, were on that day slain.”

Polk reports that millions of Hindus converted to Islam, adding that “it seems likely that the vast bulk of the converts were fleeing the tyranny of the caste system. To be born an ‘out-caste’ (dalit) was to be condemned to perpetual slavery; to convert to the brotherhood (ikhwaniyah) of Islam was to be liberated. Millions converted.” That seems exaggerated; there is a reason why the Muslim population of India is concentrated towards the country’s northwest, in the path of foreign conquest, rather than toward the south, despite the presence of Untouchables in the South. Nonetheless, Polk has a point. Indian Hindus still regard Indian Muslims as lower-caste apostates to Hinduism. On the other hand, Polk minimizes the almost unimaginable brutality of the Muslim conquest of India.

It is tempting to draw a parallel between the respective triumphs of Christianity and Islam in late antiquity. Barbarians overwhelmed the defenses of the depopulated Roman empire, and the new conquerors adopted the faith of the conquered in order to consolidate their rule. The cultural level of the Islamic world surely had surpassed that of the West at the end of the first millennium. It is conceivable that the “Golden Age” under the Abbasid Caliphate might have produced a more productive civilization had not the Mongols exterminated the population of its capital, Baghdad, in 1258 in the first of a series of wars of unimaginable cruelty. In actual history, the Church in the West succeeded in transforming the pagan invaders of Europe into prospective citizens of Christian nations, while in the East, the primal brutality of tribal society resurged in wave after wave of assaults on the centers of civilization.

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If Islam began with a cultural edge in late antiquity, Christian Europe far surpassed it by the High Middle Ages. The Islam promulgated by al-Ghazali (1058–1111) posited an absolutely transcendent God whose caprice determined the flight of every arrow and (so to speak) the spin of every electron, and abhorred the concept of human creativity; while Christianity taught a just and reasoning God, and the human capacity to participate in God’s creativity. The Renaissance and the 17th-century scientific revolution laid a foundation for Western technological superiority. The westward march of Islam stopped at Vienna in 1683. By the end of the 18th century large parts of the Islamic world were helpless before Western military power, and by the end of the 19th century Turkey stood as the world’s last redoubt of Muslim power.

After the subsequent humiliation and defeat of the Muslim conqueror-states in Egypt, the Levant, Mesopotamia, India, and Persia, we are left with a world population of 1.8 billion Muslims who nowhere have created a functioning modern state, with the partial (and fading) exception of Turkey. Most of the Muslim world is in permanent crisis. Some of its largest states, such as Pakistan and Egypt, have achieved adult literacy rates of no more than 50%, according to unofficial estimates. The broad base of society remains tribal, and the military remains the only national institution of importance. The two large Muslim countries that modernized to a significant extent, namely Turkey under Atatürk and Iran under the Shah, have reverted to Islamic rule. As I observed in my 2011 book How Civilizations Die, Muslim countries like Iran and Turkey that managed to achieve full adult literacy now face catastrophic declines in fertility. Iranian women had seven children each on average in 1979, but only 1.6 in 2017. Iran will be the first country in the world to get old before it gets rich, with devastating economic and social consequences.

Under George W. Bush and Barack Obama, America set out to fix the Muslim world, spending $7 trillion (by President Trump’s estimate) to transplant democracy there. The host rejected the transplant, though, and the so-called Arab Spring of 2011-12 degenerated into a set of wars that have no visible end. How are we to respond to societal failure on this enormous scale?

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Spencer wants us to understand that Islam has been based on conquest from its beginnings. He presents jihad as an ideological mandate from Muhammad, which subsequent Muslim leaders have followed without significant variation. As he quotes Muhammad from the Hadith:

Fight in the name of Allah and in the way of Allah. Fight against those who disbelieve in Allah. Make a holy war…. When you meet your enemies who are polytheists, invite them to three courses of action…. Invite them to (accept) Islam; if they respond to you, accept it from them and desist from fighting against them…. If they refuse to accept Islam, demand from them the jizya [a tax on unbelievers]. If they agree to pay, accept it from them and hold off your hands. If they refuse to pay the tax, seek Allah’s help and fight them.

This directive prevailed throughout Muslim history, Spencer argues. He quotes Tamerlane’s courtier, the historian and jurist Ibn Khaldun, and other authorities to the effect that Islam “is under obligation to gain power over other nations.” “These are old authorities,” Spencer adds, “but none of these Sunni schools of jurisprudence have ever reformed or rejected these directives. The Shi’ite schools teach much the same things.”

Whether the Islamic conquests first proceeded from an eruption of tribal society on the fringe of Byzantine rule, and Islam was formulated later as a conqueror’s religion, is not a trivial question. In Did Muhammad Exist?, Spencer wondered whether Islam’s founder had to be invented (later) to bring cohesion and purpose to a series of unexpected victories.

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This seems to me too simple. After the collapse of the traditional Islamic states of North Africa, the Levant, and Mesopotamia, and the failure of the Arab nationalism of Gamal Abdel Nasser, the ancient ideology of jihad figures more prominently in the Islamic world than at any time in the past thousand years. Modernization is not an option for most of the Islamic world. Unlike in China and East Asia, which emerged out of traditional society into the industrial world in a few generations, the path to modernity appears blocked. Modern Islamism seeks refuge in an idealized version of Islam’s origins.

For that reason Spencer is able to uncover a red thread linking the earliest Muslim conquests to the 2001 attacks on the World Trade Center. History may be more complex; the Islamists have repurposed the ancient concept of jihad for a war of revenge against the West. But there is a distinctly modern element in their way of waging war. For all the talk of asymmetrical warfare, the military resources at the disposal of jihadists today are trivial next to the military power of the West. The largest popular rebellion by Muslims against the West, the Algerian War of 1954-62, failed utterly in military terms. The French Army crushed the Algerian FLN. The French public could not stomach the scale of violence required to achieve victory, though, and repudiated the victory achieved in a rather dirty war. Today’s jihadists, Western-educated and attuned to the West’s own penchant for self-doubt, seek to exploit the West’s squeamishness. Hamas is the first military organization in the history of warfare to attempt to maximize casualties among its own civilian population, the better to justify Western intervention on its behalf. A photograph of one drowned migrant child in 2015 helped pry open the gates of Europe to millions of migrants, and Turkey’s president Recep Tayyip Erdogan threatened to lay the bodies of thousands of drowned children at Europe’s door unless his demands were met.

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Islam looms large in the liberal mind. Liberalism, after all, is the belief that social engineering can solve the world’s problems. Societal failure afflicting more than a billion human beings is an affront to the liberal program. Donald Trump won the presidency in part because he proposed to keep Muslim problems far from the borders of the United States. After the past 20 years, the old liberal interventionism has only a few die-hard advocates left—but one of them is Polk.

He draws a parallel as well as a moral equivalency between the jihad (Muslim attacks on the West) and crusade (Western colonization of the Muslim world). If Muslim sensibilities are enraged, Polk believes, it is because of Western mistreatment, and by accommodating Muslim feelings the West might achieve a lasting peace with Islam. Muslims, he believes, learned violence from the West. A good deal of the book reports how beastly the imperialists were to the locals. After the 1920 San Remo conference which drew French and British spheres of influence, for instance, 90,000 French troops invaded Syria and dispersed a provisional Arab government. “Thus it was in military defeat and under the shadow of French imperialism that the Syrians began their slow, painful, and often violent experience with nationalism.” The British official in charge of Iraq, Sir Arnold Wilson,

shared the British view of tribesmen. For him they were wild and colorful savages with whom one could develop a jocular relationship…. Westernized “town Arabs”—whom the British called “wogs” (wily oriental gentlemen)—were deceitful, dangerous, pompous, incapable, and best kept out of all government affairs.

Polk errs: the offensive w-word derives from the then-popular children’s doll, the Golliwog. He repeats the old canard that Winston Churchill as colonial secretary proposed to use poison gas against Iraqi rebels (Andrew Roberts shows in his Churchill: Walking with Destiny, reviewed on page 71, that he was speaking of tear gas, not mustard gas or chlorine).

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Polk’s book is riddled with errors, most of them more prejudicial than these. For example, he claims (citing the Israeli historian Benny Morris) that “In 1937, the Zionist organization drew up a plan, codenamed ‘Plan A,’ to force the Palestinians to leave…after various changes, the program became known as ‘Plan C.’” According to Polk the Israelis simply expelled 700,000 Palestinians as soon as the War of Independence broke out, and massacred hundreds of women and children at the Arab village of Deir Yassin. Not once does he mention that many of the 700,000 Arabs who left fled at the instructions of their own leaders, and that the population transfer occurred after the armies of Egypt, Syria, Iraq, Jordan, and Lebanon attacked the tiny Jewish state. The fact that multiple invasions were in progress when the population transfers occurred is never mentioned, which is rather like talking about radiation levels in Hiroshima without mentioning World War II.

Nowhere does Polk mention that 800,000 Jews were expelled from Muslim countries during and shortly after the War of Independence, and that the tiny Jewish state integrated them while the Palestinian refugees were kept apart as political hostages. He makes a great deal of the alleged Israeli massacre of Arabs at Deir Yassin, but cites none of the extensive literature contesting this accusation. Eliezer Tauber’s 2017 monograph, Deir Yassin: The End of the Myth, puts the total casualty count at 101, not the 250 cited by Polk, and shows that civilian casualties were collateral rather than intentional. Disgracefully, Polk also quotes the claim of the Israeli expatriate socialist Ilan Pappé that the Zionists deliberately injected typhoid bacteria into the water supply of the city of Acre, an unproven allegation redolent of the medieval slander that Jews poisoned wells. This is not history, but a partisan screed.

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“Throughout the age of imperialism,” writes Polk, “people in the North felt almost no compunction in oppressing, starving, or massacring peoples of the South. They justified their actions—when justification was useful or necessary—by statements that should horrify us today.” There is a good deal of truth to this, but it also is true that the United States of America did more to end imperialism than any power in history in the aftermath of World War II. It also is the case that the imperialists often were far more generous and tolerant than the locals. India is a majority Hindu nation today—and a democracy—because the British turned the balance of power against Islam, and introduced a national civil service and railway system that unified the subcontinent for the first time in its history. It is also true that the British grew opium in Bengal and forced China to buy it, with dreadful consequences about which the Chinese are justifiably rancorous. But the fact is that no one has oppressed the peoples of the Global South like other peoples of the Global South. Tamerlane, the most successful of all jihadists, goes entirely unmentioned.

Curiously, Polk counts China in the “Global North,” in part because he objects to China’s repression of its 11 million Uyghurs, a Muslim people in the country’s Xinjiang Province who speak a dialect of Turkish. During the 19th century China was one of the great victims of imperialism in the aftermath of the two Opium Wars. The once-impoverished countries of Asia have become wealthy, while the Islamic world “fell victim to ‘post-imperial malaise,’” as Polk puts it. China, Korea, and other Asian countries suffered under imperialist depredation and Japanese occupation, yet they escaped the malaise. Polk here is guilty of the logical fallacy of the True Scotsman: If countries in the Global South did not suffer from post-imperial malaise, they really must belong to the Global North.

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Contrary to Polk’s account, the Muslims and their problems simply are not that important to the West, except to the extent that they might spill over into our borders through war, migration, or terrorism. It is not difficult to control migration, which also limits the access of prospective terrorists to the West. To the extent that a Muslim country such as Iran threatens the West with weapons of mass destruction, the West—if it had the will to do so—could destroy its capacity to make war with a day’s aerial bombardment. Contrary to Polk, we do not confront the prospect of another Mao Zedong in the form of ISIS. As Robert Spencer warns, we are our own worst enemies. We lack the will to draw a bright line between the West and failing societies that we could not fix even if we spent another $7 trillion.

Paradoxically, the most powerful weapon in the hands of the jihadists is their own failure. We cannot absorb the idea that some remnants of tribal society will not modernize, but instead move directly from infancy to senescence without passing through adulthood. The best thing you can do for failing societies is: don’t become one.