ROME — Matteo Salvini basked in triumph on Monday after a thumping victory for his far-right League Party in this weekend’s European Parliament elections rendered him the dominant politician in Italy and the strongest claimant to the leadership of Europe’s populists.
But if Europe has been an incubator for resurgent nationalism in recent years, it now also feels like an active battleground.
With Europe’s decades-old project of unity increasingly in the balance, the voting energized both sides on a polarized Continent. It was a contest between angry, disaffected nationalists who want to beat back what they see as a remote and overreaching bureaucracy in Brussels, against the once-sleepy, complacent supporters of Europe looking to defend a unity that can no longer be taken for granted.
“There is a wind of positive energy,” said Mr. Salvini, whose anti-immigrant party won 34 percent of the vote in Italy. “It has brought in fresh air.”
Maybe. While the populists increased their share of seats in the European Parliament, they were denied the sort of Continent-wide earthquake they and their boosters had predicted — and their critics had feared — as turnout jumped in some places to the highest level in 20 years.
Some 75 percent of voters still backed parties that support Europe, blocking a major populist victory. Pro-Europe parties like the Greens picked up unexpected gains.
For Mr. Salvini’s critics — who see him as Europe’s version of the kind of populist strongman who now seems ascendant around the globe — the air he let in has a noxious whiff to it.
Recent elections in India, Australia and the Philippines have shown public support for tough leaders, and Mr. Salvini and other European populists are trying to push some of the same buttons. They oppose immigration, promote nationalism, blame globalization and promise a return to better, bygone eras.
But as the European elections broadly revealed, that appeal has limits, at least for now, as opponents also mobilize in an age of political volatility. Polls show the public does not want to tear down the European Union, and if many people want to change the bloc, they often disagree on how to do it.
If little else was clear from the fractured returns in Europe, the elections showed that battle lines between populists and the political establishment are still forming in a crucial — and complicated — political arena.
“The old left-right divide is being replaced by a dominant rift between populists and anti-populists,” said Zaki Laïdi, a professor and political analyst at Sciences Po in Paris.
Europe has been in a state of political ferment since the 2008 financial crisis, which created divisions between north and south, rich and poor, and generated resentments that exploded in a populist backlash after the migration crisis in 2015.
New parties or those once on the fringes in many countries suddenly found new constituencies, while the political establishment crumbled in Greece, Spain, Italy, France and elsewhere.
In the weekend voting, France’s far-right, nationalist leader, Marine Le Pen, edged out President Emmanuel Macron, who presented himself as the face of pro-European modernity.
In Eastern Europe, right-wing leaders in Hungary and Poland now lead the national governments and routinely challenge the democratic and institutional norms of the European Union. The party of Viktor Orban, the Hungarian prime minister who has eroded democratic norms, won more than half the electorate.
But in Germany and elsewhere, populist forces did not meet expectations, and the threat to a European establishment that lost votes came from strong showings by the Greens and liberals, both of whom are solidly pro-European.
In Italy, the birthplace of fascism and later a founding member of the European bloc, Mr. Salvini punched through the ceiling of even the highest expectations he had set for the returns. That outcome has already cemented his dominance in Italy’s politics.
But it was also accompanied by the collapse of another populist force — his coalition partners in the Five Star Movement — as well as the surprising revival of the pro-Europe, center-left Democratic Party, after its near-death experience in Italy’s national elections last year.
The divisive language against the European Union as the root of all the Continent’s ills “has actually galvanized people,” said Nathalie Tocci, the director of Italy’s Institute of International Affairs and a senior adviser to Europe’s foreign policy chief. “All of a sudden Europe means something.”
Ms. Tocci argued that as a result of that turnout, and a rejuvenation of the European political space by new Green voters and liberals, “the nationalists did not do as well as many feared.”
Mr. Salvini’s victory, she said, all but guaranteed Italy’s isolation in Europe and she considered his intention to form a populist group in European Parliament with up to 140 members “completely irrelevant.”
Outside of Italy, it was not clear that there was even a cohesive, pan-national populist movement to lead.
“Already within this nationalist alliance or whatever he calls it, already within that group they disagree with one another,” she said.
“Yes, they are all anti-migration but Salvini is the one who says other European countries have to take the burden,’’ she added. ‘‘You try and convince Orban about this. Be my guest. This is the point of nationalists. They are nationalists. They don’t help each other.”
Though far-right populists in Europe fell short of the worst fears of the political establishment, Mr. Salvini nonetheless captured nearly a third of votes in his country.
He did so sailing with the prevailing political winds blowing in much of the world, as autocrats in Russia and China set the pace of geopolitical competition, and President Trump acts as a one-man stress test on America’s system of checks and balances. Strong-fisted leaders, often with anti-democratic impulses, have risen to power all around.
India’s incumbent prime minister, the polarizing, right-leaning Hindu nationalist Narendra Modi, won a stunning re-election victory last week, with a populist agenda favoring India’s Hindu majority and stoking fresh fear in the country’s minority communities, especially Muslims.
President Rodrigo Duterte of Philippines, who has waged an antidrug campaign that human rights activists estimate has killed 20,000 suspected drug dealers, won more seats this month in the Senate while completely canceling the opposition from the upper house.
“This is how a democracy dies in our age, perishing on the back of a demagogue who ushers in popular dictatorship with consent of the masses and even the elite,” said Richard Heydarian, a professor of political science and author of “The Rise of Duterte: A Populist Revolt Against Elite Democracy.”
Each country had its nuances and complexities, but from a global view, it was clear which way the political axis tilted.
“There is this rightward shift of the political balance,” said Stefano Stefanini, a retired Italian ambassador to NATO.
“Leaders are able to or try to bypass institutions and the traditional systems of checks and balances by going directly to the people,’’ he said. ‘‘And that can lead to a phase where you actually do away with democracy.”
That stage had not arrived, but he worried that social media tools such as Facebook and Twitter, so adored by Mr. Trump and Mr. Salvini, could speed the process.
“Contemporary democracy runs the same risk of ancient Greece democracy: turning into tyranny,” he said.
In Europe, upheavals in identity politics — migration, globalization and an economic inequality — had led to a serious questioning of the liberal market democracy, said Roberto Menotti, a senior adviser at the Aspen Institute Italia.
“Change in general create fears, and that’s probably one simple explanation of this shift” to the right, he said. “But at the same time, it seems to me, the other big trend has been volatility.”
Parties that have been at the heart of the European political life since World War II are falling apart, and the election results eroded them further. The Brexit Party, a veritable political pop-up which sprouted only weeks ago, won about 32 percent of the vote in Britain.
“Whether this is a sort of terminal illness or just a temporary big headache of course we don’t know,” said Mr. Menotti.
What is clear from recent European history, especially in Europe, is that things change very quickly. Only five years ago, former Prime Minister Matteo Renzi, of Italy’s Democratic Party, became the toast of Europe’s left by winning more than 40 percent in European elections.
The Five Star Movement, the League’s coalition partner, became the leading party in Italy in national elections last year, but have now lost half of their support and trail the Democratic Party.
Mr. Salvini, a lifelong political operative, didn’t waste any time trying to consolidate his victory into gains that could help his longevity.
On Monday afternoon, he hit the campaign trail again, arguing in Rome that the election result gave him a mandate to renegotiate European budgetary rules imposed to bring down Italy’s dangerously inflated debt, but which would hurt his plans of introducing politically popular tax cuts.
“I will use this consensus to try to change European rules that are damaging the Italian people,” he said.