U.S. President Barack Obama has called on Europe to uphold its political unity and strengthen its contribution to the continent's collective defense.
"The entire world needs a strong and prosperous and democratic and united Europe," Obama said in a landmark speech on transatlantic unity in the German city of Hannover on April 25.
Obama's impassioned plea for European unity came days after he spoke forcefully in London against the United Kingdom exiting the European Union in what's been dubbed a "Brexit.".
The possibility of Britain leaving the EU after a June referendum, the threat posed by terrorism, and an ongoing refugee crisis have tested European unity.
"This is a defining moment, and what happens on this continent has consequences for people around the globe," Obama said.
"If a unified, peaceful, liberal, pluralistic, free-market Europe begins to doubt itself, begins to question the progress that's been made over the last several decades, then we can't expect the progress that is just now taking hold in many places around the world will continue," he said.
Obama contrasted the prosperity of today with the wars and hardship of the last century, saying that the strong ties between Europe and the United States are even more important amid today's fast global integration.
Obama enumerated the recent achievements of EU-U.S. cooperation, mentioning "pulling the global economy back from the brink of depression," the deal to rein in Iran's nuclear program, and the climate-change agreement reached in Paris last December, which he called "the most ambitious deal in history to fight climate change."
Obama also urged European NATO members to contribute their full share to the alliance, saying that "Europe has sometimes been complacent about its own defense."
He said he will insist at a July NATO summit in Warsaw that all members of the alliance must take responsibility for security.
Obama also called on European leaders to keep sanctions in place on Russia over its role in the war in eastern Ukraine until Moscow implements its obligations under the Minsk agreement.
"We must not allow borders to be redrawn by brute force in the 21st century. So we should keep helping Ukraine with its reforms to improve its economy, consolidate its democracy, and modernize its forces to protect its independence," Obama said.
He underlined that NATO has to bolster its "front-line allies in Poland, in Romania, and in the Baltic states" while also meeting "the threat of its southern flank," urging members of the alliance to increase their defense capacities.
"That's why every NATO member should be contributing its full share of 2 percent of GDP towards our common security -- something that doesn't always happen," he added.
Germany, Obama's host country and Europe's economic powerhouse, has been frequently criticized for spending well below the target on defense capabilities.
Obama also urged Europe and NATO allies to do more in the fight against the extremist group Islamic State.
He said the United States would send up to 250 more special-forces military trainers to Syria to help rebels fight IS, which he called "the most urgent threat to our nations."
Obama also cited a need for balance between security and privacy, touching one of the sore spots in the relationship between Germany and the United States.
Documents disclosed in 2013 by former U.S. National Security Agency (NSA) contractor Edward Snowden embarrassed the Obama administration, revealing that even German Chancellor Angela Merkel's own telephone conversations had been tapped by the U.S. side.
Obama said that while surveillance programs remain an effective weapon in the fight against terrorism, he acted to reform such programs to ensure they are "upholding our values like privacy."
"By the way, we include the privacy of people outside of the United States. We care about Europeans' privacy, not just Americans' privacy," he added.
Obama also credited Merkel, who was sitting in the audience, for welcoming refugees.
Obama said that Merkel, who has been facing criticism from other EU members for her stance and has seen the support for her Christian Democratic Union slip to its lowest levels in years, "demonstrated real political and moral leadership" in accepting more than 1.1 million people fleeing war and misery.
"What's happening with respect to her position on refugees here, in Europe -- she's on the right side of history on this," Obama told the audience.
He decried an "us-versus-them" mentality that breeds animosity toward immigrants, Muslims, and others.
Obama's speech came as some German officials and commentators have claimed that his administration has done little to help Merkel as Europe struggles with its biggest migrant crisis since World War II.
Obama confirmed in Hannover that the United States would take in 10,000 Syrians this year.
Obama and Merkel later met with Prime Minister David Cameron, French President Francois Hollande, and Italian Prime Minister Matteo Renzi to discuss the fight against IS in Syria and Iraq, and the refugee crisis.