The last decade has in particular brought one setback after another.

As the EU turns 60 amid a divorce from Britain and other mid-life crises, the question is increasingly not how it can bounce back, but how it can survive.

Today's European Union is the product of efforts led by France and Germany in the wake of World War II to bring peace to a continent that had seen centuries of war.

But the political and economic union ushered in by the March 1957 Treaty of Rome that leaders will celebrate this week is in many ways less united than ever.

Divisions abound over migration, populism and the economy, combined with worries about its place in the world and life after Brexit.

While the mantra of EU founding father Jean Monnet was that Europe would be forged in crisis, fears are now that it may be fatally weakened.

“This mantra, you couldn't hear it any more during the last years in the Brussels bubble," said Stefan Lehne, visiting solar at Carnegie Europe.

"There is not just one big crisis but a multiplicity of very severe and complicated challenges, and I think this changes things,” Lehne told AFP.

Lehne said it was more likely the EU would eventually cease to be in its current form, becoming an "ever looser union" instead of an ever closer one, as the EU's treaties famously envisaged.

'Holy Roman Empire'

“I think sometimes of the Holy Roman Empire that continued to exist for hundreds of years after it had sort of died politically,” he added.

In Rome on Saturday, EU leaders are set to endorse a "multispeed" Europe that allows some countries to push ahead with cooperation while others lag behind, but which some call a slow disintegration.

After years of burying their heads in the sand, European leaders have finally acknowledged they face an existential crisis.

New European Parliament chief Antonio Tajani said this week that the "European project has never seemed so far away from the people as it does today".

But what makes today's crises different from those that the organisation formerly known as the European Economic Community faced in its early years?

In the 1960s there was the 'empty chair crisis' when France under General de Gaulle blocked decision making, and de Gaulle's repeated 'non' to Britain joining.

Then the oil crisis in the 1970s and repeated referendums on the treaties all posed major challenges.

Still, Europe managed to emerge triumphant from the Cold War and then rapidly expanded in the early 2000s.

It has also pushed through with major projects like the euro and the Schengen passport-free area -- but increasingly tensions over these big achievements are what is driving the EU apart.

“The crises we face today fundamentally call into question the point of the European project,” said Frederic Allemand of Luxembourg University.

“Clearly peace is still the frontispiece, but apart from that, what kind of social and economic model do we want in Europe?”

'Muddling through'

The last decade has in particular brought one setback after another.

Following the 2007-8 financial crisis, growth has remained sluggish and unemployment high. The eurozone debt crisis almost forced Greece out and German-led austerity has caused a legacy of bitterness.

Europe has also failed to halt the carnage in Syria and the conflict in Ukraine, both sources of tension with Russia, while a series of Islamist terror attacks have transformed the security environment.

A wave of 1.4 million asylum seekers in 2015 and 2016, largely sparked by the Syria war, has meanwhile shattered the EU's facade of solidarity as Eastern Europe blamed Germany's open-door policy for the influx.

“Never before have I seen such fragmentation and also such little convergence in our union,” European Commission chief Jean-Claude Juncker said last year.

Many in Brussels hope that unity in the face of Brexit negotiations, and clarity after key elections in France and Germany, will help to focus minds by the end of 2017.

But they are already divided over what comes next.

Some want to push ahead with defence, especially amid insecurity over new US President Donald Trump's commitment, or the economy, while others in the former Soviet east want to ease off on integration.

But most will still want to keep the advances that the last 60 years have brought, said Hendrik Vos, a professor at the University of Ghent.

“It is not the most efficient and not the most beautiful way to escape from a swamp — but you can escape a swamp by muddling through and that's the way the EU operates," he said.

Five major quotes on Europe

From the dream of a United States of Europe to recent crises, the history of the European project has inspired landmark declarations by European leaders.

Here is what some said:

1946: Winston Churchill “If Europe were once united in the sharing of its common inheritance, there would be no limit to the happiness, to the prosperity and glory which its three or four hundred million people would enjoy... We must build a kind of United States of Europe,” the two-time British prime minister said on September 19, 1946, in a speech at the University of Zurich.

1950: The Schuman Declaration “The contribution which an organised and living Europe can bring to civilisation is indispensable to the maintenance of peaceful relations... Europe will not be made all at once, or according to a single plan. It will be built through concrete achievements which first create a de facto solidarity,” Robert Schuman, the French foreign minister, said on May 9, 1950, proposing the creation of the European Coal and Steel Community.

1979: Margaret Thatcher “I want my money back!” the British prime minister was widely quoted as saying on November 30, 1979 — Winston Churchill's birthday — calling for the British contribution to the then EEC budget to be reduced, prompting one of the most serious crises besetting the European project.

The phrase she actually used after a meeting of the European Council in Dublin was, “We want a very large proportion of our own money back.”

1995: Francois Mitterrand “Nationalism is war, and war is the past. But it is not only the past. It could be our future. You are the guarantors of our peace and of our security,” the French president told the European Parliament on January 17, 1995.

2016: Angela Merkel “Do you seriously believe that all the euro states that last year fought all the way to keep Greece in the eurozone — and we were the strictest -- can one year later allow Greece to, in a way, plunge into chaos?” the German chancellor asked in a television interview on February 29, 2016, regarding Europe's refugee crisis.

She went on to vow: “It's my damn duty and obligation to do everything possible for Europe to find a united path.”