Brooding in 1938 about the degree to which the future has a distressing way of taking us by surprise, the Anglo-French author Hilaire Belloc, so admired by his English Catholic contemporaries, ventured the startling prediction that the principal unexpected development lying in wait for the Europeans of his own day was nothing other than “the return of Islam,” “the most formidable and persistent enemy which our civilization has [ever] had.” At the time, with Nazi, Fascist, and Communist totalitarianisms casting an ever-lengthening shadow across the continent, that prediction must surely have smacked of the eccentric. But not today, as Philip Jenkins makes abundantly clear in this stimulating, informative, meaty, and judicious book, the third in his much-praised Future of Christianity trilogy.

On this matter, gloomy talk (à la Samuel Huntington) about an impending “clash of civilizations” would indeed appear to be rife. “Jihad in Europe,” “Eurabian civil war,” “Islamism as the new Nazi-Fascism,” a “Eurabian nightmare” of “rapid Islamization” destined “within a few” decades to produce nothing other than “a Muslim continent”-book titles and pamphleteering slogans scratch away obsessively at what seems now to have become an exceedingly widespread itch. As recently as 2004, an Arabist of even Bernard Lewis’s stature could bluntly assert that “current trends show Europe will have a Muslim majority by the end of the twenty-first century at the latest.... Europe will be part of the Arab west-the Maghreb.” With that prognostication, the irrepressible Colonel Qaddafi, it seems, would himself be inclined to agree. And, among Catholic commentators, George Weigel can contemplate “a Europe in which the muezzin summons the faithful to prayer from the central loggia of St. Peter’s in Rome, while Notre Dame has been transformed into Hagia Sophia on the Seine-a great Christian church become an Islamic museum.” Append to all of that some of the arresting statistics with which Jenkins punctuates his account (that a full fifth of the population of Vienna, for example, is now Muslim; that the most popular name today for baby boys in Brussels is Muhammed, etc., etc.), and the implausible begins to harden into the plausible, and the plausible to modulate into the indubitable.

But if Jenkins is quick to recognize the prevalence and power of this “Apocalypse Now” genre of commentary on the changing religious and cultural landscape of Europe, it is not his purpose here to endorse it. Instead, having first probed the essentially ideological agendas lurking behind some of the more gloomy prognostications of the day, he then proceeds along a trajectory that draws into the discussion, along with matters religious, a broad array of demographic, economic, ethnic, and social factors. As a result, he succeeds in engineering a corrective complexification in our understanding of what is actually taking place on the European religious scene, as well as a more diffident and nuanced assessment of what may conceivably lie ahead.

So far as agendas are concerned, he alerts us to the fact that jeremiads about the destructive impact of European secularism, the concomitant decline of European Christianity, and the looming triumph of Euro-Islam (themes that, though distinct, persistently tend to converge) may really be directed, like Tacitus’s Germania, less to the subject matter ostensibly under discussion than to the deportment of one’s fellow citizens at home. For Belloc and G. K. Chesterton, the evocation of the continued vitality and power of Islam was really a way of highlighting the cost for a once-Christian England of the corrosively secularizing impact of Enlightenment values. Something similar can be said of Weigel and of Michael Novak-who in the aftermath of the 2005 riots in Paris insisted that “a very large part of the ‘European crisis’ is the crisis of the Enlightenment.” This is perhaps less a commentary on Europe than a stern warning to Novak’s complacent fellow countrymen in the United States.

That said, and our consciousness having thus been suitably raised, Jenkins moves on to attend to the facts on the ground in Europe itself. There, so far as demographics are concerned, fertility rates in the Western European countries have certainly fallen below (sometimes well below) the replacement rate of 2.1 children per woman, while the birthrate among the immigrant Muslim population is, indeed, considerably higher. But gleeful Islamist predictions that Muslim dominance will eventually be assured because immigrant Muslim women are systematically “outbirthing” native European women fail to take into account the demographic changes already underway among Muslim populations. A dramatic and accelerating drop in birthrates is already evident in the countries from which so many of the Muslim immigrants have characteristically been drawn. In Turkey, Iran, Algeria, and Tunisia, for example, that rate has already fallen below the replacement level; and in Morocco, too, it appears to be closing in on that mark. Jenkins reminds us, moreover, that a significant proportion of the immigrant population moving from Africa to Europe has in fact been Christian rather than Muslim-often Christian of a markedly evangelical, fundamentalist stamp. The eastward expansion of the European Union has also promoted an influx into the more secularized societies of Western Europe of a sizable labor force from countries to the east where Catholic observance has persisted at traditionally high levels. Today, as a result, there are more Polish than Gaelic speakers in Ireland, and in England more Poles than Pakistanis.

A similar complexity characterizes other, less readily quantifiable features of the changing European religious scene. As far as specifically religious commitments are concerned, it would be premature to conclude either that a fervently rigid fundamentalism of the Wahhabist type possesses some sort of manifest destiny among European Muslims, or that the future career of European Christianity is necessarily destined to be downhill all the way. Both communities of believers are far from being monolithic, either in the nature of their religious commitments or in the degree of fervor characteristic of their religious practice. Both exhibit considerable diversity; both are fraught with complex internal tensions. The more puritanical and evangelistic forms of Islam do appear to resonate strongly with the younger generation of European Muslims. But nonobservant “cultural” Muslims far outnumber the militantly neo-orthodox. In France today, for example, only about 5 percent of the Muslim population attend mosques on a regular basis. Nor, for that matter, is the new Muslim population expanding into some sort of religious vacuum. While institutional statistics tend to promote the idea that European Christianity is “terminally ill,” we should not overlook the presence of countertrends like the startling growth in the number of those undertaking pilgrimages to such traditionally sacred sites as Lourdes, Knock, or Santiago de Compostela. If changes in the religious configuration of Europe are undoubtedly exposing fragilities of one sort or another, some are now suggesting that the most striking of these fragilities may be those observable in the once unassailable structure of European secularism.

On the last point Jenkins has much to say that is interesting. And nothing more so than his cautious ventilation of the possibility that, in the ongoing struggle against the “blinkered secularism” so deeply embedded in the Western European psyche, Euro-Christians of the future may find themselves not altogether out of sympathy with the moral and religious sensibilities of their Muslim fellow citizens. The likely upshot, then-at least according to Jenkins? That the real threat of Muslim terrorism notwithstanding, “perceptions of a naked clash of civilizations are wide of the mark.” Nor, dismal institutional statistics to the contrary, should we be too quick to dismiss the underlying vitality of Euro-Christianity. The real question, instead, may concern the strength, vitality, and enduring power of the once robust secularist ideology that has played so dominant a role in the societies of Western Europe ever since it rose to hegemony during the Century of Light.