The terrorist assault on the French satirical magazine Charlie Hebdo on Jan. 7 may have been organized by al Qaeda’s affiliate in Yemen. But the attack, along with another at a Paris kosher market days later, was carried out by French Muslims descended from recent waves of North African and West African immigration. Well before the attacks, which left 17 dead, the French were discussing the possibility that tensions with the country’s own Muslim community were leading France toward some kind of armed confrontation.

Consider Éric Zemmour, a slashing television debater and a gifted polemicist. His history of the collapse of France’s postwar political order, “Le suicide français,” was No. 1 on the best-seller lists for several weeks this fall. “Today, our elites think it’s France that needs to change to suit Islam, and not the other way around,” Mr. Zemmour said on a late-night talk show in October, “and I think that with this system, we’re headed toward civil war.”

More recently, Michel Houellebecq published “Submission,” a novel set in the near future. In it, the re-election of France’s current president, François Hollande, has drawn recruits to a shadowy group proclaiming its European identity. “Sooner or later, civil war between Muslims and the rest of the population is inevitable,” a sympathizer explains. “They draw the conclusion that the sooner this war begins, the better chance they’ll have of winning it.” Published, as it happened, on the morning of the attacks, Mr. Houellebecq’s novel replaced Mr. Zemmour’s at the top of the best-seller list, where it remains.

Two days after the Charlie Hebdo killings, there was a disturbing indication on Le Monde’s website of how French people were thinking. One item about the killing vastly outpaced all others in popularity. The reactions of Europe’s leaders was shared about 5,000 times, tales of Muslim schoolchildren with mixed feelings about 6,000, a detailed account of the Charlie Hebdo editorial meeting ended by the attack, 9,000. Topping them all, shared 28,000 times, was a story about reprisals: “Mosques become targets, French Muslims uneasy.” Those clicks are the sound of French fear that something larger may be under way.

France’s problem has elements of a military threat, a religious conflict and a violent civil-rights movement. It is not unique. Every country of Western Europe has a version. For a half-century, millions of immigrants from North and sub-Saharan Africa have arrived, lured by work, welfare, marriage and a refuge from war. There are about 20 million Muslims in Europe, with some 5 million of them in France, according to the demographer Michèle Tribalat. That amounts to roughly 8% of the population of France, compared with about 5% of both the U.K. and Germany.

Such a migration is not something that Europeans would have countenanced at any other moment in their generally xenophobic history, and the politicians who permitted it to happen were not lucky. The movement coincided with a collapse in European birthrates, which lent the immigration an unstoppable momentum, and with the rise of modern political Islam, which gave the diaspora a radical edge.

Just why Europe has had such trouble can be partially understood by contrasting it with the U.S. Europe’s welfare states are more developed and, until recently, more open to noncitizens, so illegal or “underground” immigration has been low. But employment rates have been low, too. If Americans have traditionally considered immigrants the hardest-working segment of their population, Europeans have had the opposite stereotype. In the early 1970s, 2 million of the 3 million foreigners in Germany were in the labor force; by the turn of this century, 2 million of 7.5 million were.

Europe was not just disoriented by the trauma of World War II. It was also demoralized and paralyzed by the memory of Nazism and the continuing dismantling of colonialism. Leaders felt that they lacked the moral standing to address problems that were as plain as the noses on their faces—just as U.S. leaders ducked certain racial issues in the wake of desegregation.

Europeans drew the wrong lessons from the American civil-rights movement. In the U.S., there was race and there was immigration. They were separate matters that could (at least until recently) be disentangled by people of good faith. In Europe, the two problems have long been inseparable. Voters who worried about immigration were widely accused of racism, or later of “Islamophobia.”

In France, antiracism set itself squarely against freedom of speech. The passage of the 1990 Gayssot Law, which punished denial of the Holocaust, was a watershed. Activist lobbies sought to expand such protections by limiting discussion of a variety of historical events—the slave trade, colonialism, foreign genocides. This was backed up by institutional muscle. In the 1980s, President François Mitterrand’s Socialist party created a nongovernmental organization called SOS Racisme to rally minority voters and to hound those who worked against their interests.

Older bodies such as the communist-inspired Movement against Racism and for Friendship Among the Peoples made a specialty of threatening (and sometimes carrying out) lawsuits against European intellectuals for the slightest trespasses against political correctness: the late Italian journalist Oriana Fallaci for her post-9/11 lament “The Rage and the Pride,” the philosopher Alain Finkielkraut for doubting that the 2005 riots in France’s suburban ghettos were due to unemployment, the Russia scholar Hélène Carrère d’Encausse for speculating about the role of polygamy in the problems of West African immigrants.

Speech codes have done little to facilitate entry into the workforce for immigrants and their children or to reduce crime. But they have intimidated European voting publics, insulated politicians from criticism and turned certain crucial matters into taboos. Immigrant and ethnic issues have become tightly bound to the issue of building the multinational European Union, which has removed vast areas of policy from voter accountability. “Anti-European” sentiments continue to rise.

So impressed were the Europeans with their own generosity that they failed to notice that the population of second- and third-generation immigrants was growing bigger, stronger, more unified and less inclined to take moral instruction. This is partly a demographic problem. Since the fall of the Berlin Wall, Western Europe has had some of the lowest birthrates of any civilization on record. Without immigration, Europe’s population would fall by a hundred million by midcentury, according to U.N. estimates.

When mass immigration began, Europeans did not give much thought to the influence of Islam. In the 1960s, there might have been worries that a North African was, say, a Nasserite Arab nationalist, but not that he was a would-be jihadist. Too many Europeans forgot that people carry a long past within them—and that, even when they do not, they sometimes wish to. Materialistic, acquisitive, averse to God and family, Europe’s culture appeared cold, dead and unsatisfying to many Muslims. It failed to satisfy a lot of non-Muslims too, but until they ran out of borrowed money with the 2008 crash, they could avoid facing it squarely.

Europeans didn’t know enough about the cultural background of Muslims to browbeat them the same way they did the native-born. Muslims felt none of the historic guilt over fascism and colonialism that so affected non-Muslim Europeans. They had a freedom of political action that Europeans lacked.

As European politics grew duller and the stakes lower, many political romantics looked enviously at the aspirations of the Muslim poor, particularly regarding Palestine. You could see a hint of this last weekend in the BBC journalist who interrupted a mourning Frenchwoman, distraught about the targeting of Jews for murder at a kosher supermarket, to say that “the Palestinians suffer hugely at Jewish hands.”

In a world that prized “identity,” Muslim immigrants were aristocrats. Those who became radicalized developed the most monstrous kind of self-regard. A chilling moment in the most recent terrorist drama came when the TV network RTL phoned the kosher supermarket where the Malian-French hostage-taker, Amedy Coulibaly, was holding his victims at gunpoint. He refused to talk but hung up the phone carelessly. The newspaper Le Monde was able to publish a transcript of the strutting stupidity to which he then gave expression:

“They’re always trying to make you believe that Muslims are terrorists. Me, I’m born in France. If they hadn’t been attacked elsewhere, I wouldn’t be here…Think of the people who had Bashar al-Assad in Syria. They were torturing people…We didn’t intervene for years…Then bombers, coalition of 50,000 countries, all that…Why did they do that?”

The Muslim community is not to be confused with the terrorists it produces. But left to its own, it probably lacks the means, the inclination and the courage to stand up to the faction, however small, that supports terrorism. In 1995, there were riots among French Muslims after the arrest of Khalid Kelkal of Lyon, who had planted several bombs—in a train station, near a Jewish school, on a high-speed rail track. In 2012, when Mohamed Merah of Toulouse was killed by police after having gunned down soldiers, a rabbi and three Jewish elementary-school children, his brother professed himself “proud,” and his father threatened to file a wrongful-death suit against the government.

And when Charlie Hebdo printed a memorial cover this week that had a picture of its controversial cartoon character “Muhammad” on it, it was as if the attacks had never happened: Muslim community spokesmen, even moderate ones, issued dire warnings about the insult to them and their coreligionists. To many Muslims in France and the rest of Europe, the new drawings were evidence not that the terrorists had failed to kill a magazine but that the French had failed to heed a warning. Impressive though the post-attack memorial marches were, “the working classes and the North African and West African immigrant kids weren’t there,” as the president of France’s Young Socialists told the newspaper Le Temps.

It may seem harsh to criticize the French in their time of grief, but they are responding today with tools that have failed them in previous crises. They reflexively look at their own supposed bigotry as always, somehow, the ultimate cause of Islamist terrorism, and they limit their efforts to making minority communities feel more at home.

The mysterious riots of 2005 in France—which lasted for almost three weeks, during which the rioters made no claims and put forward no leaders—were chalked up to deprivation. The French media responded with an effort to hire more nonwhite news anchors and reporters, and the government promised to spend more in the suburbs. Now, after the murders in Paris, the contradictions continue to accumulate:

• On religion: Mr. Hollande has insisted that the attacks have “nothing to do with Islam.” At the same time, Prime Minister Manuel Valls speaks of “moderate Islam” and rails against “conservatism and obscurantism”—as if the violence had everything to do with Islam, and even with religious devotion in general.

• On spying: Some in the French government blame intelligence failures, since the secret services tracked the Charlie Hebdo killers Said and Chérif Kouachi until last summer. But government officials boast of about their principled unwillingness to legislate a “Patriot Act a la française”—even as they draw daily on intelligence gathered by the U.S.

• On religious hatred: Justice Minister Christiane Taubira has announced an all-out assault on “racism and anti-Semitism,” promising that those who attack others because of their religion will be fought “with rigor and resolve.” In theory, this sounds like a promise to protect Jewish shoppers from getting killed at their neighborhood grocery stores. In practice, it will mean placing limits on any inquiry into the inner dynamics of Muslim communities and may wind up increasing the terrorist threat rather than diminishing it.

What continues is the deafness of France’s government and mainstream parties to public opinion (and popular suffrage) on the issues of immigration and a multiethnic society. Mr. Hollande’s approval ratings have risen since the attacks, but they are still below 30%. In January 2013, according to the newsweekly L’Express, 74% of the French said that Islam “is not compatible with French society.” Though that number fell last year, it is almost certain to be higher now.

Voters all across Europe feel abandoned by the mainstream political class, which is why populist parties are everywhere on the rise. Whatever the biggest initial grievance of these parties—opposition to the European Union for the U.K. Independence Party, opposition to the euro for Alternative für Deutschland, corruption for Italy’s 5 Star Movement—all wind up, by voter demand, placing immigration and multiculturalism at the center of their concerns.

 In France, it is the Front National, a party with antecedents on the far right, that has been the big beneficiary. In the last national election, for seats in the European Parliament, the FN, led by Marine Le Pen (daughter of the party’s founder, Jean-Marie Le Pen), topped the polls. But the ruling Socialists froze the Front National out of the recent national ceremonies of mourning, limiting participation in the Paris rally to those parties it deemed “republican.” This risks damaging the cause of republicanism more than the cause of Le Pen and her followers.

Acts of terrorism can occur without shaking a country to its core. These latest attacks, awful as they were, could be taken in stride if the majority in France felt itself secure. But it does not. Thanks to wars in Iraq, Syria and Yemen, thousands of young people who share the indignation of the Kouachis and Coulibaly are now battle-hardened and heavily armed.

France, like Europe more broadly, has been careless for decades. It has not recognized that free countries are for peoples strong enough to defend them. A willingness to join hands and to march in solidarity is a good first response to the awful events of early January. It will not be enough.

The Wall Street Journal