BRUSSELS -- The Rome Declaration, signed by the leaders of 27 EU member states on March 25, marked the 60th anniversary of the bloc's founding Rome Treaty with a vow for continued unity after Britain leaves the European Union.
But the Rome Declaration also contains language that, according to some critics, could threaten European unity by creating what politicians have described as a "two-speed" European policy.
Others say a better description would be a "multispeed" Europe.
With the exception of Britain, all EU member states signed the Rome Declaration -- stating that they "will act together, at different paces and intensity where necessary, while moving in the same direction."
Supporters: Two-Speed Europe Would Allow Progress
Supporters of a two-speed (or multispeed) Europe say it will give member states more freedom to form partial alliances and set policies when it is impossible reach a unanimous consensus in the EU.
That, they argue, is particularly important if the EU continues expanding into the Balkans and becomes a bloc of more than 30 countries. They say reaching unanimous decisions with so many member states would be much more difficult.
Luxembourg Prime Minister Xavier Bettel said at the Rome summit over the weekend that he would "rather have a two-speed Europe than a dead-end and no speed" Europe.
"When a country says 'I don't want to,' I can say: 'Well, too bad. Don't block me. Let me get on with it with others,'" Bettel said.
Critics: Two-Speed Policy Would Create Separation, Not Unity
Detractors argue that by allowing differentiation, the bloc is abandoning one of its core principles -- the principle of attaining equality through deeper integration.
The detractors say that rather than creating a two-speed Europe, there is a risk of creating two separate Europes within the EU.
European Council President Donald Tusk, the former prime minister of Poland, told leaders at the Rome summit that he had lived half his life behind the Iron Curtain when Europe was divided into the Cold War alliances of East and West.
"Back then, that really was a two-speed Europe," Tusk warned the Rome gathering.
Who Would Lead A Two-Speed Europe?
Judy Dempsey, an expert on European affairs at Carnegie Europe, says the main issues are the idea of what a "two-speed" or "multispeed" Europe really means and which countries might be included in the first-tier and second-tier groups.
Experts agree that the idea of a "core" group led by the six founding European Community members -- the so-called "inner six" -- is not tenable.
"It's clear that the two speeds will have to be led by the eurozone countries," Dempsey tells RFE/RL, noting that the 19 EU countries now using the euro currency constitute a "qualified majority" needed for the approval of legislation by the European Council of Ministers.
For those countries, Dempsey says the key issue would be a fundamental rethink of fiscal structures -- how far to move toward greater fiscal union and tighter monetary union.
On the other hand, she says, the nine EU states that currently are not in the eurozone may resent being categorized as second-tier EU members.
Poland's current government has already warned that the idea of a two-speed Europe would result in the "breakdown" and "liquidation of the European Union in its current sense."
Dempsey says that if a two-speed Europe materializes, the reactions of Poland and other non-eurozone countries will create a conundrum for Germany -- which supports a multispeed Europe but "has been very careful about making the idea an official mantra."
"Berlin has to be very careful about the kind of language it uses because it wants to bring everyone on board," she says. "And that means trying to get an agreement that won't give the impression that Germany is actually shaping Europe."
Multispeed Europe? Or Two-Speed Europe?
Roland Freudenstein, deputy director of the Wilfried Martens Center for European Studies, says he doesn't think Europe is moving toward a two-speed policy at all -- despite the rhetoric of politicians who support the idea.
"I think what we're talking about is multispeed or varied integration," Freudenstein tells RFE/RL. "I don't believe we are talking about a core group and a marginal group. That is not what is going to happen and that's not what should happen."
Freudenstein notes that German Chancellor Angela Merkel, after years of stressing "maximum unity" within the EU, is now publicly backing the idea of a "multiple-speed" Europe.
"She doesn't mean that there should be one core that moves forward in all directions and a periphery," he says.
"Most member states like this concept of a multispeed Europe -- certainly France, the Netherlands, and some of the Scandinavian countries," Freudenstein says, adding that Southern European member states "have no problem with it."
Freudenstein says he thinks Poland's objections are based on a misunderstanding of the issues. "There are not going to be two classes" of EU members," he insists.
What Groupings Could Emerge On Different Issues?
To a large degree, the experts agree that the concept of a multispeed Europe is likely to lead to internal groupings based around the EU's different challenges.
In fact, they argue, multispeed Europe already exists on issues like the eurozone and Schengen-area countries that have abolished passport controls across mutual borders.
The experts say some new blocs could form on defense projects -- with Sweden, Poland, Germany, Denmark, and the Netherlands working together in that area.
On the issue of security, they say multispeed policy would allow France, Germany, and the Netherlands to improve cooperation on intelligence sharing.
Other countries would likely create alliances over the issues of asylum laws and deepening their cooperation on justice and home affairs.
"These groups are not going to be identical," Freudenstein says. "There is not going to be one core group."
For countries that are trying to join the EU, experts say a multispeed policy could lead to the creation of new structures for accession.
Is Multispeed Europe The Solution To EU Problems?
Rosa Balfour, acting director of the Europe Program of the German Marshall Fund of the United States, says she is skeptical about the debate on a two-speed or multispeed Europe.
Balfour remains unconvinced that the idea of a multispeed Europe will solve key problems now faced by the EU, such as the migrant crisis or the European debt crisis.
"I think the solution is finding policy answers to the current challenges and then devising what format is best to push through those policies," Balfour explains.
"It's all very well to say that we can move at different speeds," she adds. "But to do what? It's the policies that really need to be thought through."