BERLIN — From France and Britain to Denmark and Greece, voters may have just put the brakes on the Golden Age of European integration.

Stunned leaders across the region were grappling Monday with the aftershocks of Sunday’s vote for the 751-member European Parliament that saw a record number of seats go to once-fringe parties bitterly opposed to a united Europe. The results presented the region’s mainstream parties with a reality check: Maybe Europeans aren’t quite as eager as their leaders think they are to forge a joint future.

In the decades after World War II, nations across the region embraced a common path, boldly moving to open borders, create a common currency and cede national powers to a European Union authority based in the region’s administrative capital of Brussels. With little more than a plane ticket and a plan, Polish plumbers could find work in Paris or London. Italian engineers could labor inside German auto factories. Greek cooks could set up shop in Barcelona, Copenhagen or Amsterdam.

But after four years of economic devastation from Europe’s debt crisis, the love-thy-neighbor shtick is wearing thin for millions of European voters. Even pillar countries such as France, now mired in economic stagnation and hopelessness, are increasingly blaming the E.U. for their woes.

At the same time, the results suggested a strong backlash to German-led demands for tough fiscal austerity and economic reforms that voters across the region are blaming for massive unemployment, particularly in still-troubled Greece.

Indeed, by voting to send a new sea of nationalists and extremists from the far right and left to the region’s centerpiece legislature, voters have effectively put the foxes in the hen house, giving a new platform to those who want to turn back the clock on European integration.

At the least, analysts say, the vote could give new momentum to a push being led by British Prime Minister David Cameron to reclaim some powers ceded by national governments to Brussels, effectively reversing the trend of the past several decades toward integration.

The outcome of the elections were “a massive rejection of the European Union,” Marine Le Pen, whose anti-EU French nationalists came in first Sunday in their best showing ever, told supporters after the results came out. She added that the French, at least, “don’t want to be led from the outside anymore.”

Though anti-EU parties staged their strongest showing ever, they are still on track to secure less than a third of the seats in the European parliament, not enough to create absolute gridlock. In fact, analysts say one byproduct of the vote could be a move by pro-EU parties from the center-right and center-left to work together more in parliament to promote the integration agenda.

Yet the surging fringe groups could still pose a danger to certain key pieces of legislation – particularly the Free Trade Agreement being negotiated between the E.U. and the United States.

“If you bring in a big bloc like this, the risk is they are able to sometimes bring with it more mainstream parliamentarians to stop certain issues, and that could certainly apply to free trade,” said Mats Persson, director of the London-based think tank Open Europe.