Eight years ago, when I moved to London to run this newspaper's European bureau, I found my domestic life unfolding in the epicentre of a cultural upheaval – some were already calling it a civilizational clash – that would dominate the politics of Europe, and then of North America, for years to come.

By that point, my North London neighbourhood had changed. The sidewalks of its haphazard shopping street, Holloway Road, were peppered with women in hijab (and occasionally full niqab) and men in beards and shalwar kameez. Pubs and fish-and-chips shops had been displaced by Turkish kebab houses, money-transfer joints and Internet cafes with opaque Arabic signs.

This had been an immigrant neighbourhood for 140 years, but these latest immigrants attracted more attention. It sometimes seemed as if Islam were everywhere. Our after-school babysitter, a French girl from an Alpine village who had been partial to all-night raves, abruptly converted to the faith of her Algerian friends and took to covering her head and praying five times a day. It made her no less attentive to our children, but more sombre and less willing to eat our food.

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Even as my children befriended the Usamas and Leilas in their primary-school classes and the parents of those children became our doctors and shopkeepers, the neighbourhood showed a more ominous face. Our local Muslim house of worship, the Finsbury Park Mosque, was raided by hundreds of police just before my arrival. Its imam – a one-eyed, hook-handed Egyptian-born former mujahedeen fighter who called himself Abu Hamza and was known in the tabloids as "hooky mullah" – was arrested on 16 charges of incitement of murder, terrorism and race hatred after harbouring al-Qaeda activists and delivering sermons calling for the murder of non-Muslims in Islamic lands.

And then, less than a year later, suicide bombs tore through the public-transit system, blowing both legs off one of my neighbours. The attacks were committed by British-born Muslims from Leeds who didn't appear all that different from some of the guys we saw on Holloway Road.

Given those experiences, who wouldn't look askance at the new neighbours? The appearance of visibly different immigrants from a minority religion, who tended to be poor and prone to conservative beliefs, was enough of a shock – that their influx coincided with the rise of an extremist political movement obsessed with Western presence in the "land of Islam" and bent on violence made it seem more than just shocking.

For a while, I myself would cast a sidelong glance at the bearded guy on the bus and think, "Could he be one?" I'd look at the packs of children accompanying the covered women and wonder if our values – especially of gender and sexual equality – would someday become a minority creed. For all of us, it was hard not to quietly ask: Were these pockets of violence and radicalism an inevitable extension of these immigrants' everyday beliefs? Were they all potential extremists, commanded by their religion to resist cooperation and integration? Was it always going to be like this?

A surging 'Muslim tide'

It was around that time that a new "Muslim tide" argument appeared on blogs, YouTube videos, in newspaper columns and bestselling books, offering an easy "yes" to these questions.

Yes, it said, these immigrants are different from earlier groups. They are driven by their religion, not by the laws and social codes of their new homes. They are reproducing at an unusually rapid pace, with fertility rates far higher than those of exhausted Western populations, and are poised to become a majority. And, yes, that is a danger because they are loyal not to their host society but to Islam, which, as these writers and activists see it, is not so much a faith as an ideology of conquest.

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These claims began with obscure blog posts and work by hardcore anti-Muslim activists, but around 2005 they spread to popular books by authors such as Bruce Bawer, Christopher Caldwell and Thilo Sarrazin. Eventually, they also erupted into national politics in a dozen countries.

They turned single-issue politicians, such as the Dutch anti-Muslim firebrand Geert Wilders, into powerful figures. They became a motif in Quebec politics: "Muslim tide" rhetoric lay behind Parti Quebecois leader Pauline Marois's push to ban Muslim garb, as it did behind Saguenay mayor Jean Tremblay's declaration that PQ candidate Djemila Benhabib was trying to "dictate how we behave" and impose her non-Christian "rules" on his province.

The "Muslim tide" was a dominant trope in the U.S. Republican Party's leadership race, with at least four major candidates parroting Newt Gingrich's line about a secret plot among ordinary Muslims to impose "stealth sharia" on America. This summer, a circle of Congressmen made claims, on no credible evidence, that the most prominent Muslim officials in the U.S. government are somehow tied to the Egyptian Muslim Brotherhood.

Perhaps not coincidentally, violent attacks on mosques have increased sharply. And this week, a guilty verdict was handed down to Anders Behring Breivik, who produced the Muslim-tide ideology's first terrorist atrocity. When he killed 77 people in a truck bombing and shooting spree in Oslo last summer, he left behind a 1,518-page manifesto that explained his act: Most of it was a pastiche of passages by activists such as Pamela Geller, Robert Spencer, Gisele Littman and Canadian Mark Steyn – none of whom has ever explicitly advocated violence, but whose visions of a civilizational invasion became his justification for mass killing.

His manifesto also included the words used in his legal defence: "The individuals I have been accused of illegally executing are all … supporters of the anti-European hate ideology known as multiculturalism, an ideology that facilitates Islamisation and Islamic demographic warfare … I must be must be allowed to prove that I executed these traitors in order to prevent them from continuing to contribute to the ongoing process of cultural and demographical genocide and extermination."

The millions of otherwise moderate and reasonable people who have bought, and sometimes enjoyed, books by the same authors who inspired Mr. Breivik probably don't believe their more ornate notions of a Muslim-immigrant plot to take over the West. Rather, they are seeking a narrative to explain the simultaneous appearance of Muslim immigrants and Islamic political violence in the headlines.

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The Catholic scare

The unease I felt on the sidewalks and buses of our London neighbourhood was not a novel sensation.

If I had lived there a dozen decades earlier, I would have watched the streets fill with suspicious-looking men and women wearing identity-concealing head scarves. Their families were widely believed to belong to an alien civilization. They segregated themselves from the native-born population, were guided by a deeply conservative religion that seemed at odds with modern values, and had the world's highest reproduction rate. And they were using my neighbourhood to plot a wave of terrorist attacks that killed more Londoners and caused more political alarm than the jihadist attacks of the new millennium.

Today, the Irish Catholics I'm describing are simply part of the neighbourhood's mix, their pubs and churches an integral part of London's culture. But for seven decades, Roman Catholics and East European Jews were widely regarded as disloyal, impossible-to-integrate members of an outside civilization. And not just in Britain: If you lived in Canada or the United States in 1950, you would have been aware of a certain type of immigrant seemingly determined to impose their values on their new home – guided by a religion that was not so much a faith as an ideology of conquest.

One of the bestselling books of the period, American Freedom and Catholic Power by Paul Blanshard, argued that Catholic culture is "a survival of mediaeval authoritarianism that has no rightful place in the democratic American environment." The book was endorsed by Bertrand Russell and Albert Einstein, and had great influence in Congress and academia.

In Canada, Italians, along with most other southern European Catholics, were classed as "non-preferred." One government memo of the time said of the Italian Catholic worker: "even his civilization seems so different that I doubt if he could even become an asset to our country." Outside of Quebec, it was quite normal to describe Catholic immigrants as an unwelcome and dangerous addition – and their "civilization" probably appeared (and in some ways was) more alien to Anglo-Americans than that of most urban Muslims today.

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These statements sound like grotesque religious prejudice today, but to many they seemed well-justified at the time. After all, most Catholic countries had fallen to fascism or religious extremism; Catholic immigrant neighbourhoods were crime-ridden, violent and impoverished; and the worst acts of North American terrorism to that point had been committed by people from Catholic backgrounds. Who wouldn't look askance at their Catholic neighbours?

We have forgotten this history. And we have forgotten that the same things were said about the waves of East European Jewish immigrants before the war. The phrase "Judeo-bolshevism" was that era's equivalent to today's "Islamo-fascism," and was frequently directed against Jewish immigrants.

Part of this was classic anti-Semitism, but from 1880 onwards there was a new anti-Semitism directed at Jews as immigrant outsiders: They wore odd clothes, were poor and generally illiterate, clustered themselves in self-segregated neighbourhoods, were almost all Orthodox and culturally conservative, were associated in the public mind with crime and radicalism, and were reproducing at a great pace. These seemingly commonsense observations about Eastern Jews soon allowed much of the Western public to blandly tolerate the greatest mass murder in history.

If we want to avoid repeating history, we need to recognize its patterns around us.

And then, the facts

One reason why the "Muslim tide" hypothesis has gone unchecked for so long is because we simply didn't know much about the immigrants from Muslim-majority countries in our midst. They were too new: Almost half of Canada's million Muslims, for example, are immigrants, two thirds of whom arrived after 1990.

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But the last three or four years have seen a revolution in our understanding of Muslim populations in the West, with a dozen large-scale studies, surveys and projections providing a detailed picture of this minority group – their activities, beliefs, integration patterns and sources of political extremism and moderation. These studies show that many ideas behind the "Muslim tide" (including some held by Muslims themselves) are myth, not fact.

Behind the "Muslim tide" myth lie three core beliefs. First is the claim that their populations are growing so rapidly that Muslims will become majorities everywhere. Because Muslim immigrants tend to come from poor, rural regions prone to overpopulation, they often arrive with large families and have many children soon after settling in their new country. This has created the perception that they will soon swamp countries with low fertility rates.

But this is a gross misinterpretation of what is happening to Muslim populations. Muslim-majority countries are experiencing the fastest decline in fertility and population growth in the world. Witness Iran, the world's only Islamic theocracy, where mothers had an average of 7 children each in the 1980s; that number has now dropped to 1.7, below the averages in France and Britain (at least 2.1 is required for a country to have population growth). In Turkey, the average has fallen to 2.15 children; in Lebanon, to 1.86; in the United Arab Emirates, 1.9. In Indonesia, home to the world's largest Muslim population, the family size is about to slip below two children.

This rapid decline in fertility is even more pronounced among Muslims who migrate to the West. Muslims in Canada have on average 2.4 children per family. That's above Canada's average of 1.7, but it appears that Muslims born in Canada – that is, the children of immigrants – go on to have only about two children each. And by the next generation, they will be close to the Canadian average.

Claims that Europe will be overrun by a "Muslim majority" are based on similar misreadings. The most comprehensive projections of Islamic populations indicate that Europe's Muslim population will reach about 7.1 per cent by 2030, at which point Muslims on the continent will be averaging only 2 children per family. The total Muslim population could peak at around 9 per cent, but better education and citizenship policies would make it lower.

Falling fertility rates are a sign of integration: They entail the use of birth control, the empowerment of women and a broadly secular understanding of the world. And they point to a broader (if not universal or consistent) pattern of integration – dispelling a second core belief of the "Muslim tide," which holds that Muslims are less likely, or interested, in integration than previous groups.

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Indeed, a major 2009 study of Canadian immigrants found that skin colour, not religion, is the determining factor in integration: "If anything," it concluded, "South Asian and Arab and West Asian Muslims report somewhat higher levels of integration than co-ethnics in other religions."

And while Muslims are currently more conservative on issues such as tolerance of homosexuality and the rights of women, their views are vastly more liberal than in their countries of origin – and tend to align with Western views in the second generation. As far as identifying themselves as Muslims first and Canadians (or Americans or Britons) second, they say this about as much as devout Christians do. And they express loyalty to their home country and its secular institutions at the same, sometimes greater, rates as native-born citizens.

This is not entirely a rosy picture. Muslim immigrants in some places – notably Britain – are lagging behind in cultural integration. Like Jewish and Catholic immigrants before them, they are experiencing pockets of isolation and conservatism, and the economic effects of discrimination and lack of fluency. Anti-semitism and obsessions with the Middle East are far too popular among the second generations in many countries.

But what we see is not a vast historic exception, rather a repeat of the pattern followed by earlier religious-minority immigrants.

Eating kebabs in London

That is all well and good, you might say, but what about the suicide bombers? Islamic extremism in the West remains a serious threat, even if it has diminished from its peak a decade ago.

Here, too, we have a new understanding. A number of very large new studies of the views and motives of terrorists and extremists – including an expansive one by the British intelligence agency MI5 – has confirmed what terrorism experts have long believed: That extremism is a political movement, based on territorial ambitions (specifically, a belief in the inviolate "land of Islam") not rooted in the religious beliefs of the wider community.

Over and over, we find that those driven to extremism are not very religious and not very tightly linked to their surrounding immigrant communities; they tend to be middle-class loners, often with criminal histories. The most devout, while culturally conservative, are the least politically extreme.

What does distinguish Islamic extremists in the West is their belief that "Islam" and "The West" are distinct and separate entities that should never meet. This belief in a clash of civilizations, ironically, is the one thing that unites Islamic extremists with the "Muslim tide" authors and politicians. Christopher Caldwell, Thilo Sarrazin and Melanie Phillips all express admiration for the strength and coherence of Islamic "civilization" and despair for what they see as an overly secular West. Mr. Breivik was an outright admirer of Osama Bin Laden. And no wonder: What unites the ideologies of al-Qaeda and of the "Eurabia" and "Muslim tide" writers is a common belief that there is one creature called "the Muslim" and another called "the Westerner."

Yet there is no such distinction. Muslims are adopting the universal values of our society in the same way (not always easy) as other religious minorities.

The shisha bar and the kebab shop are becoming part of Western culture, much like espresso and Yiddish expressions – but there is no threat to our core values.

If we believe that our culture is so weak that it can be threatened by a small group of generally poor and vulnerable immigrants, then what is it worth?

That became apparent in London. I soon realized, as I came to know the Pakistanis and Turks around me, that they and their children are the principal victims of both of these political ideologies. Islamic extremism is a threat to Muslim families. The "Muslim tide" literature, and the distrust it provokes, only amplifies this threat. We need to fight back against both of these dangerous belief systems.

Adapted from The Myth of the Muslim Tide: Do Immigrants Threaten the West?

Doug Saunders is The Globe's international-affairs columnist. He just completed eight years as the paper's London-based European bureau chief.