"When an insecure, malleable, relativistic culture meets a culture that is anchored, confident, and strengthened by common doctrines," Mr. Caldwell writes, "it is generally the former that changes to suit the latter." The book is not a polemic; it is at once nuanced and blunt, serious and witty, while also avoiding what Mr. Caldwell calls "the preemptive groveling that characterizes most writing about matters touching on ethnicity." He does not advocate positions but instead offers reflections on a mix of trends, misunderstandings and self-delusions.

He also ruminates on far more than the increasing radicalization of generations of Muslim immigrants. Just as Edmund Burke's "Reflections on the Revolution in France" (1790) predicted a dire fate for the mass insurrection then aborning, Mr. Caldwell looks with alarm at Europe's continuing rejection of itself. Without a rejection of the religion and culture that sustained Europe for centuries, he says, the immigration troubles might never have occurred, or at least would not have been so severe: His verdict is suicide rather than murder.

The author notes that even the prominent German philosopher Jürgen Habermas, who is an atheist, has acknowledged that "Christianity, and nothing else, is the ultimate foundation of liberty, conscience, human rights, and democracy, the benchmarks of Western civilization. To this we have no other options. We continue to nourish ourselves from this source. Everything else is postmodern chatter."

Yet much of Europe has discarded its historic religious underpinnings as irrelevant at best, harmful at worst. Even the memory of what a religiously ordered society was like has seemed to disappear, Mr. Caldwell observes. "A good definition of religion" for most modern Europeans, he says, might be "an irrational opinion, strongly held."

Most European elites, though, have not debated seriously the potential effects of introducing into this land of postmodern chatter millions of devout believers in another religion, one previously seen as antagonistic to European culture. As Mr. Caldwell says, Europe's elites seem hardly to have considered that the ethical views they pride themselves on have little meaning when divorced from Christian origins.

Many Europeans are determined to defend their values- witness France's ban on headscarves in schools-but it is hard to defend what you cannot define. "There is no consensus, not even the beginning of a consensus," Mr. Caldwell writes, "about what European values are." When the Netherlands decided not long ago to try to define its values and inculcate them in prospective new residents, it ended up producing a ghastly naturalization packet that included a video that featured "gays expressing affection in public, and bare-breasted women on the beach." Welkom, immigrants.

In his reflections on Europe's slide into a sort of secular suicide, Mr. Caldwell notes the key role played by that most religious impulse: guilt. He argues that the dominant moral mood of postwar Europe was "repentance for two historical misdeeds, colonialism and Nazism." Over the decades, guilt has festered into "a sense of moral illegitimacy" and a "self-directed xenophobia" that now shapes the continent's response to immigration.

Originally, the reasons given for encouraging mass immigration to Europe were economic-a means of remedying Europe's purported labor shortage and, eventually, of bolstering economies obliged to fund generous pension plans. Immigrants "would emerge from the desiccated and starving hamlets of the Third World and ride to the rescue of the retirement checks and second homes, the wine tastings and snorkeling vacations, of the most pampered workforce in the history of the planet," Mr. Caldwell writes. Such economic rationales proved to be chimeras, though. Nowadays, with majorities in many countries consistently opposed to immigration, a new justification has had to be found: the flat assertion that immigration and asylum policies are "nonnegotiable moral duties that you don't vote on," or perhaps even discuss.

If much about immigration is nonnegotiable, then problems that appear to be caused by immigration must instead be understood as the result of "some quirk or accident," Mr. Caldwell says, "never immigration itself." But there is nothing quirky about it. The problems are not local but everywhere evident, across national boundaries, because they challenge Europe's very idea of itself. "If you understand how immigration, Islam, and native European culture interact in any western European country," Mr. Caldwell notes, "you can roughly predict how they will react in any other-no matter what its national character, no matter whether it conquered an empire, no matter what its role in World War II, and no matter what the provenance of its Muslim immigrants." As for how governments respond to immigration pressures within their own countries, officials tend to look to the French model of assimilation or the British model of multiculturalism, depending "on which country had suffered rioting less recently."

All this may seem to cry out for a loud and long, soul-searching debate, but don't count on it. Discussion about immigration is decidedly circumscribed in countries where postcolonial guilt has led to taboos against criticism of anything putatively Muslim. The riots and slayings over a Danish newspaper's publication of a few cartoons depicting the Prophet Muhammad put an entire continent on notice to watch its words. Mr. Caldwell gives little advice and few predictions about what lies ahead. But he does address the question of "whether you can have the same Europe with different people. The answer is no."

---Dr. Marshall is a senior fellow at Hudson Institute's Center for Religious Freedom and the editor of "Blind Spot: When Journalists Don't Get Religion."