Pope Francis warned world leaders on Friday that the European Union "risks dying" without a clear vision for the future.
The pontiff addressed European Union leaders at the Vatican ahead of the bloc's 60th anniversary celebrations, scheduled to take place in Rome on Saturday.
"When a body loses its sense of direction and is no longer able to look ahead, it experiences a regression and, in the long run, risks dying," Francis said.
Celebrations marking 60 years of Europe's economic and political cohesion have been dampened by Britain's impending departure from the union. EU leader Jean-Claude Juncker called the country's 2016 decision to leave the bloc a "failure and a tragedy."
"We are not in the best form and shape we could be in," he admitted in an interview with the BBC on Friday.
Britain's vote, dubbed "Brexit," is among a number of blows to hit the EU in recent years, which include an ongoing economic crisis in Greece, rising mainstream support for the far right, and an influx of migrants that has sparked debates over resettlement.
Some have argued that the bloc may simply be "failing forward," by which incremental reforms follow a period of turmoil. In his address, Pope Francis reminded the union's leaders that it was the horrors of World War II that gave rise to European solidarity in the first place.
The bloc's founding fathers, he said, "were inspired by the hope of a better future and were determined to pursue it by avoiding the rise of new conflicts."
Six nations signed the 1957 treaty to establish the EU, which grew to a partnership of 28 countries. Britain's departure, expected to take effect by the summer of 2019, moves the tally down to 27. Francis warned that others may follow if the bloc fails to establish a "patrimony of ideals and spiritual values."
The pontiff called European solidarity the "best antidote against the vacuum of values of our time, which provides a fertile terrain for every form of extremism," referencing Wednesday's terror attack in London.
He also decried "the tragedy of walls and divisions," echoing previous statements he has made seemingly directed at President Donald Trump. "It is not enough to handle the grave crisis of immigration of recent years as if it were a mere numerical or economic problem, or a question of security," Francis said.
The EU could recover its strength, the pope argued, by investing in the wellbeing of its people and pursuing a peaceful future. "Its success will depend on its readiness to work together once again," he said, "and by its willingness to wager on the future."