By Valentina Pop 

For European Union leaders, Saturday's gathering in Rome to mark the 60th anniversary of the bloc's founding treaty was to be an unvarnished celebration of a successful experiment to rebuild a continent scarred by two world wars.

But Brexit, economic malaise, immigration, Russian hostility, U.S. indifference and growing nationalist sentiment across Europe have ruined the birthday party.

Those looming problems, signified most pointedly by the absence of British Prime Minister Theresa May at Saturday's commemoration, have laid bare deep divisions between the bloc's richer and poorer nations, between fiscal hawks in the north and debtor nations in the south, and between former Communist nations in the east and member nations in the west.

Keeping the six nations that originally signed the Treaty of Rome in 1957 on the same page--let alone the 22 that followed--now looms as a daunting challenge.

The eurozone economic crisis, which peaked in 2012, badly hurt growth across Europe, increased unemployment and exposed a lack of competitiveness among the 19 EU members who use the euro and make up the zone.

The migration debacle three years later exposed the bloc's simmering divisions, as governments publicly squabbled over who was to blame, and Central and Eastern European countries balked at allowing Brussels to set country quotas for taking refugees.

Now the bloc looks on nervously as the far-right, anti-EU Marine Le Pen is a front-runner in the first round of French presidential elections next month and as a populist, anti-Islam, anti-euro party in Germany is set to make gains in parliamentary elections in September.

For some EU members, the cure for the bloc's ills is another galvanizing idea that, in some form, could be codified in the declaration that is to culminate this weekend's commemoration.

But bold proposals, such as a common army or a Europe-wide pension system, have drawn no support from EU leaders. Ahead of the summit, the idea of looser degrees of integration in the EU also hasn't garnered enough backing among the leaders.

The treaty's original signatories--France, Germany, Italy and the Benelux states--repackaged as "multispeed Europe" the longstanding idea of having the eurozone move ahead with more economic and political integration. Meanwhile, the eight remaining members of the bloc after Brexit would have looser ties.

Former Italian Prime Minister Enrico Letta says "multispeed Europe" is "the only way to keep the 27 united, allowing the core countries, the founders of the eurozone, to go further if they want."

The bloc, he argues, has become too heterogeneous and the divisions over the balance of power too deep for the union to function efficiently.

But Central and Eastern European nations continue to oppose "multispeed Europe," and have rejected efforts to enshrine it in this weekend's concluding document.

Even though the degree of integration among EU members today varies widely--with not all EU countries sharing the euro and borderless travel, for instance--these countries have long feared that such an arrangement would mean fewer subsidies.

More recently, they also view it as punishment for their reluctance or refusal to take in refugees from Muslim countries.

Radoslaw Sikorski, a former Polish foreign minister, says while "multispeed Europe" is in many ways a reality today, some politicians in his region equate it with "two-speed Europe," where the periphery would have no say over decisions made at the core.

"Two-speed is something core countries see as necessary to preserve the eurozone and something that the periphery considers to be a power grab," he says.

Mr. Sikorski says the bloc's east-west economic divide is narrowing and won't last. In a few years, some Central European nations, including the Czech Republic, will no longer qualify for EU subsidies for poorer regions, he said.

Citing the victory of incumbent Prime Minister Mark Rutte over anti-EU candidate Geert Wilders in Dutch elections earlier this month, Mr. Sikorski believes the nationalist winds buffeting the EU will subside.

"I hope Brexit and [U.S. President Donald] Trump, Marine Le Pen and Russian cyberwarfare have frightened us sufficiently to think about what we are about to lose," he said.

But perhaps not yet. On Thursday, Polish Prime Minister Beata Szydlo said she wouldn't sign Saturday's planned declaration unless it reflects her country's demand that the unity of the bloc be preserved.

Greek Prime Minister Alexis Tsipras also threatened this week to withhold his approval unless there was progress in negotiations with international creditors.

At the meeting's end, there probably will be a "moderately ambitious" declaration, former Finnish Prime Minister Alexander Stubb said. "But it won't change the world like the original Rome declaration."

Write to Valentina Pop at valentina.pop@wsj.com

(END) Dow Jones Newswires

March 23, 2017 12:37 ET (16:37 GMT)