LONDON — Nearly every day seems to bring a new horror to the streets of Western Europe, leaving innocent men, women and children dead or broken, fueling political and social tensions and creating what some are already calling the summer of anxiety.
Death and injury have been dealt out by truck, ax, handgun, machete and bomb. The victims have included families out for a night of fireworks on the glittering French Riviera, teenagers hanging out at a McDonald’s, tourists on a train and pop music fans at a Sunday night concert.
Three of five attackers in less than two weeks professed loyalty to the Islamic State, but none appear to have been directed by the radical group, and all of the assaults seemed to blur the line between ideological terrorism and violence driven by anger, grudge or mental instability.
That very murkiness — the absence of a centrally organized plot or a singular villain to blame — has made it all the more difficult for France, Germany and the rest of Europe to know how to respond.
The lack of straightforward answers has made things trickier at a time of political flux in Europe. Even before the latest string of attacks, the Continent was seeing a rise in nationalist and anti-immigrant sentiment, and far-right parties were using the atmosphere to try to gain new legitimacy and power. Populist, anti-immigration sentiment was a powerful factor in Britain’s vote last month to leave the European Union.
The recent surge in high-profile violence has only given further opportunities to those who advocate taking a tougher line on immigration by Muslims, in many ways echoing the platform being promoted by Donald J. Trump in his presidential campaign in the United States. Over the weekend, Prime Minister Viktor Orban of Hungary spoke highly of Mr. Trump, saying the Republican nominee’s proposals for fighting terrorism were just what Europe needs.
In France, which displayed remarkable unity after two terrorist attacks in 2015, there has been growing political infighting and finger-pointing since the July 14 attack in Nice that killed 84 people. In Germany, the latest attacks have further strained ties between Chancellor Angela Merkel’s conservative party and its ally in the southern state of Bavaria, where there has long been simmering opposition to her decision last year to admit one million asylum seekers.
Concern about the security and social ramifications of a new surge in migrants coming to Europe from Syria, Afghanistan and other poor and war-torn countries has left the European Union with reduced leverage in dealing with President Recep Tayyip Erdogan of Turkey as he cracks down on opponents in the wake of a failed coup this month. Mr. Erdogan had agreed to a deal with the European Union to hold back the tide of asylum seekers, a deal that Europe is deeply reluctant to endanger, especially with new security concerns attached to the migrants.
The same sorts of attacks have occurred elsewhere, including last month in Florida. But the concentration of attacks over less than two weeks in Europe has given the issue particular resonance on the Continent.
Finding answers is in part a familiar security and intelligence challenge. But it is also in some cases a problem of immigration, assimilation and tolerance. And it is a reminder of the lure of the burst of fame, or infamy, available to troubled, violence-prone people in an age of social media and instant global communication.
For some, he said, that is jihad. “It can happen in Orlando and Nice,” he said, “and without a lot of prior consultation or structure or networking.”
Ali Sonboly, the 18-year-old who killed nine people in Munich on Friday, may have been Iranian-German, but he took his inspiration in part from Anders Behring Breivik’s massacre five years ago in Oslo, Norway, which was driven by the hatred of a white supremacist. Mr. Sonboly “wanted to make his mark as an individual” by hacking into Facebook to entice people to McDonald’s, “the intertwining of complete barbarity and utter modernism,” Mr. Heisbourg said.
Mr. Sonboly was acting not as a state or an organization but as an individual, and individual actors are extremely hard for security services to stop. Yet their individual acts, captured on smartphones and sent around the world, can resonate louder than any gunshot or explosion.
The attack in Nice, France, was carried out by a Tunisian-born man with a rented truck. It has set off a new battle over blame and added another volatile element to the early stages of a presidential campaign where the governing Socialists, led by President François Hollande, are falling further behind the right and far-right.
The fierce and open debates over security and accountability are a sharp contrast to the reaction in France to last year’s attacks, when there was an effort to create a sense of political and national solidarity in the face of terrorism.
There is vivid anger at what appears to be the inability of the government to keep people safe. The local government in Nice, which leans right, issued a blunt broadside against the Socialist government and specifically the interior minister, Bernard Cazeneuve, for failing to have adequate security in place on Bastille Day. Mr. Cazeneuve was also accused of pressuring the local government to massage the numbers to make it appear that there were more safety provisions in place.
Mr. Cazeneuve called the allegations part of a “vile” and “calumnious” campaign to defame him and his ministry, but his job may be on the line.
In Germany, three of the four recent attacks have been carried out by recent immigrants, two of them Syrian, and all of them Muslims. Three of the four were in Bavaria, which was the first reception center for more than a million migrants last year seeking asylum, and where the governing Christian Socialists have been an early and persistent opponent to Ms. Merkel’s open-door policy, despite their close alignment to her Christian Democrats.
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The German far-right party, Alternative for Germany, has been divided, but this spate of attacks could help the party, which under a new leader, Frauke Petry, has shifted to emphasize issues like opposition to Islam and immigration. With seats in eight state parliaments, the party is expected to gain seats in the Bundestag, or national parliament, next year.
The national political reactions are playing out against a backdrop of global change in which terrorism is only one element.
“The world has been changing and we see that manifested in many ways, with new power centers, the power of the individual and the corporation, the disenfranchised finding a new voice and a sense that the governing infrastructure is no longer fit for purpose in today’s world,” said Xenia Wickett of Chatham House, a London foreign-policy research institution.
Institutions, she said, are struggling to deal with new challenges from Islam, inequality, terrorism and globalization. “We’re trying to manage that change and people don’t like change,” she said. “That’s the new normal, and it makes us very anxious until we can find a new one.”