At the start of this year, Spain was thought to be Europe’s political outlier — a country immune from the advances of the far right.

But after the Vox party cracked open the door to parliament in April and came in third in national elections on Sunday, Spain can be singled out for something else: Among major European countries, it is where the far right is gaining ground most quickly.

“You have been the stars of the greatest, most dazzling political act in Spanish democracy,” jubilant Vox leader Santiago Abascal told voters after his party won 15 percent of the seats, the best showing for the far right since Spain’s transition from dictatorship in the 1970s.

The Socialist party claimed the most votes in Sunday’s elections — but there was no obvious path for any party on the left or right to easily form a government in Spain’s fragmented system.

The Socialists, led by acting prime minister Pedro Sánchez, won 120 of 350 seats in the Congress of Deputies. The center-right Popular Party, which has been plagued by corruption scandals, came in second with 88 seats. And Vox finished with 52, compared with 24 seats in elections in April.

Even as the results promised to continue Spain’s months-long political deadlock, they jettisoned long-held conventional wisdom about Spanish politics — that memory of Francisco Franco’s dictatorship would limit the appeal of the extreme right.

Experts say Vox has succeeded in positioning itself as the defender of the country’s unity — countering the separatist push in Catalonia, a volatile crisis that mainstream parties have been unable to resolve.

Vox has also drawn some support because of a modest backlash over immigration and cultural issues. The party is stridently anti-Muslim and takes a harsh stance against feminism and gay rights.

It has mirrored an aspect of President Trump’s playbook, calling for better fortifications of Spanish autonomous zones in North Africa. And some of its immigration rhetoric resembles that of other nationalist parties across Europe.

Two of Europe’s highest-profile far-right leaders, Italy’s Matteo Salvini and France’s Marine Le Pen, congratulated Vox on Twitter for its election performance.

But, above all, Vox’s emergence has been based on a distinctly Spanish issue.

“Vox is mainly linked to specific factors dealing with the Catalan conflict, and that makes Vox a bit of a different party compared to others on the radical right,” said Juan Rodríguez Teruel, an associate professor of political science at the University of Valencia.

Teruel said that Spain is still largely a culturally liberal and pro-immigrant society and that for Vox to make inroads on issues beyond Catalonia, it will have to use its higher profile to more widely spread “illiberal views among Spanish people.”

While Spanish prime ministers on the right and left have tried to push back against the pro-independence movement, Vox politicians have argued the country hasn’t used its full powers to deal with the separatist threat. In the weeks before the elections, protesters in Catalonia were back on the streets, with sometimes-violent protests — images that were widely shared among Spanish far-right voters on social media.

“There is a sense of impotence” about Catalonia, said Charles Powell, director of the Madrid-based Elcano Royal Institute, an international relations think tank. “The TV footage everyone saw, the violence on the streets of Barcelona, with young [people] beating up the police — that really had a big impact.”

In the run-up to the vote, Vox leader Abascal said he wanted Catalan’s regional president, Quim Torra, arrested for affiliation with “terrorist” groups causing violent unrest. He said Catalonia should be stripped of its existing degree of autonomy. During a debate, Abascal mentioned the “wasteful spending” on autonomous regional governments, quoting figures for the cost that Madrid’s El Pais newspaper called “questionable” and suggesting that spending jeopardized pensions. No other party leaders challenged Abascal’s claims.

A former councilman for Spain’s center-right Popular Party, Abascal broke away to found Vox in 2014.

Hailing from northern Spain’s formerly restive Basque region, Abascal was raised in a political family threatened by the armed separatist group ETA, which killed more than 800 people — including judges, journalists and politicians — in its campaign for independence. Abascal reportedly watched his father, a councilman from the center-right Popular Party, deal with death threats. Abascal went into politics at 18 and was forced to have constant bodyguards.

On Sunday night, supporters chanted and sang songs from the early ’70s outside Vox headquarters in Madrid until Abascal appeared on a platform to address the crowd.

“We haven’t just altered the political map of Spain,” Abascal said. “We have told the left that the story isn’t over, and that they don’t have moral superiority. We have the same right as they do to be represented without being stigmatized like they are doing in the media. We have contributed to perfecting Spanish democracy.”

Harlan reported from Rome and Rolfe from Madrid.