BERLIN — The attacks in Oslo on Friday have riveted new attention on right-wing extremists not just in Norway but across Europe, where opposition to Muslim immigrants, globalization, the power of the European Union and the drive toward multiculturalism has proven a potent political force and, in a few cases, a spur to violence.

The success of populist parties appealing to a sense of lost national identity has brought criticism of minorities, immigrants and in particular Muslims out of the beer halls and Internet chat rooms and into mainstream politics. While the parties themselves generally do not condone violence, some experts say a climate of hatred in the political discourse has encouraged violent individuals.

“I’m not surprised when things like the bombing in Norway happen, because you will always find people who feel more radical means are necessary,” said Joerg Forbrig, an analyst at the German Marshall Fund in Berlin who has studied far-right issues in Europe. “It literally is something that can happen in a number of places and there are broader problems behind it.”

Last November a Swedish man was arrested in the southern city of Malmö in connection with more than a dozen unsolved shootings of immigrants, including one fatality. The shootings, nine of which took place between June and October 2010, appeared to be the work of an isolated individual. More broadly in Sweden, though, the far-right Sweden Democrats experienced new success at the polls. The party entered Parliament for the first time after winning 5.7 percent of the vote in the general election last September.

The bombing and shootings in Oslo also have served as a wake-up call for security services in Europe and the United States that in recent years have become so focused on Islamic terrorists that they may have underestimated the threat of domestic radicals, including those upset by what they see as the influence of Islam.

In the United States the deadly attacks have reawakened memories of the Oklahoma City bombing in 1995, where a right-wing extremist, Timothy J. McVeigh, used a fertilizer bomb to blow up a federal government building, killing 168 people. That deadly act had long since been overshadowed by the events of Sept. 11, 2001.

According to Mr. Forbrig, isolated right-wing groups in Europe would rise up and then quickly disappear from the ’60s into the ’90s. But in recent years far-right statements have appeared to lose much of their post-World War II taboo even among some prominent political parties.

A combination of increased migration from abroad and largely unrestricted movement of people within an enlarged European Union, such as the persecuted Roma minority, helped lay the groundwork for a nationalist, at times starkly chauvinist, revival.

Groups are gaining traction from Hungary to Italy, but it is particularly apparent in northern European countries that long have had liberal immigration policies. The rapid arrival of refugees, asylum seekers and economic migrants, many of them Muslims, led to a significant backlash in places like Denmark, where the Danish People’s Party has 25 out of 179 seats in Parliament, and the Netherlands, where Geert Wilders’s Party for Freedom won 15.5 percent of the vote in the 2010 general election.

Mr. Wilders famously compared the Koran, the holy book of Islam, to Adolf Hitler’s “Mein Kampf.” Both the Danish and Dutch right-wing parties are backing precarious minority governments while not directly participating by having ministers, and inching toward mainstream acceptance in the process.

Friday’s attacks were swiftly condemned by leaders from across the political spectrum in Europe. Germany’s Chancellor Angela Merkel was particularly sharp in speaking out against what she called an “appalling crime.” The sort of hatred that could fuel such an action, she said, went against “freedom, respect and the belief in peaceful coexistence.”

Yet some of the primary motivations cited by the suspect in Norway, Anders Behring Breivik, are now mainstream issues. Mrs. Merkel, President Nicolas Sarkozy of France and Prime Minister David Cameron in Britain all recently declared an end to multiculturalism. Multiculturalism “has failed, utterly failed,” Mrs. Merkel told fellow Christian Democrats last October, though stressing that immigrants were welcome in Germany.

Perhaps the most surprising about-turn came in Britain, a country that has long considered itself among the most immigrant-friendly in Europe until a series of coordinated bomb attacks in London six years ago. In one of his most noticed speeches, Mr. Cameron told the Munich security conference in February that the country’s decades-old policy of multiculturalism had encouraged “segregated communities” where Islamic extremism can thrive.

France, a fiercely secularist state where all religion is banned from the public sphere, was long isolated and berated for its staunch opposition to the laissez-faire of multiculturalism. Girls who show up in public schools there with the Muslim headscarf are suspended, as are teachers or any other employees in the public sector.

If Mr. Sarkozy appeared to soften his understanding of official secularism, or “laïcité” earlier in his political career, even toying with the idea of affirmative action, he has recently scrambled to backtrack. He held a nationwide debate on “national identity” last year and earlier this year banned Muslim full-face veils like niqab, as well as the burqa.

That hasn’t stopped the far-right National Front, now led by Marine Le Pen, the daughter of its founder, to surge in opinion polls, with some surveys predicting that she might make it into next year’s presidential runoff. She compared Muslims praying in the streets outside overcrowded mosques to the Nazi occupation, and decries the European Union and the euro.

Earlier this month the daily newspaper Berliner Zeitung reported that neo-Nazis were attacking the offices of the far-left Left Party with increasing frequency. In the former East German state of Mecklenburg-Vorpommern, statistics showed that there were 30 such attacks in the first half of 2011 compared to 44 attacks in all of 2010.

Due to its Nazi past, Germany keeps a watchful eye on right-wing extremists, and the parties of the far right have a hard time gaining traction, with no representatives in Parliament. In Finland, the True Finns, a populist nationalist party founded in 1995, became the third largest party represented in the Finnish Parliament after winning 19 percent of the vote in April. And Norway’s Progress Party, a right-wing populist party, is the second largest in the country, winning 23 percent of the vote in the last parliamentary election in September 2009.

“The Norwegian right-wing groups have always been disorganized, haven’t had charismatic leaders or the kind of well-organized groups with financial support that you see in Sweden,” said Kari Helene Partapuoli, director of the Norwegian Center against Racism. “But in the last two or three years our organization and other antifascist networks have warned of an increased temperature of debate and that violent groups had been established.”

But neither does Norway exist in a vacuum. Its right-wing scene is connected to the rest of Europe through the Internet forums where hate speech proliferates and through right-wing demonstrations that draw an international mix of participants.

“This may be the act of a lone, mad, paranoid individual,” said Hajo Funke, a political scientist at the Free University in Berlin who studies rightist extremism, referring to the right-wing fundamentalist Christian charged in connection with the killings, “but the far-right milieu creates an atmosphere that can lead such people down that path of violence.”