HAMBURG, Germany — President Trump brought a starkly populist and nationalistic message to Europe on Thursday, characterizing Western civilization as under siege and putting the United States on a potential collision course with European and Asian powers that embrace a more cooperative approach to the world.

Speaking in Warsaw ahead of his arrival here in Germany for a contentious Group of 20 summit, Trump delivered an address that was both provocative and short on specifics – arguing that Western values are increasingly imperiled by “radical Islamic terrorism” and extremism and casting himself as a champion in a vaguely defined clash of cultures.

“The fundamental question of our time is whether the West has the will to survive. Do we have the confidence in our values to defend them at any cost?” Trump said, speaking at a monument to a past struggle, the 1944 Polish resistance to Nazi occupation in World War II. “Do we have enough respect for our citizens to protect our borders? Do we have the desire and the courage to preserve our civilization in the face of those who would subvert and destroy it?”

Later in the day, Trump took to Twitter to proclaim that “THE WEST WILL NEVER BE BROKEN. Our values will PREVAIL.”

TENSIONS WITH GERMAN CHANCELLOR

The fiery address to a friendly crowd stacked with supporters of Poland’s populist ruling party did not define those Western values in any detail, however, and was devoid of the kind of explicit endorsement of democratic ideals common among past U.S. presidents. Unlike President Obama last year, for example, Trump did not direct any criticism at his host, Polish President Andrzej Duda, for a crackdown on press freedoms and other restrictive policies.

And on the eve of a planned 30-minute meeting with Russian President Vladimir Putin, Trump again refused to say definitively whether Russia had interfered in the U.S. elections, as U.S. intelligence agencies strongly assert, though he did rebuke Moscow for its “destabilizing activities” in Ukraine and elsewhere.

Trump’s foreboding message in Warsaw stood in stark contrast to the more optimistic notes struck by Germany’s Angela Merkel and other European leaders at the start of the G-20 summit here in Hamburg. The day’s events included the formal announcement of a trade agreement between the European Union and Japan, a deal akin in size to the North American Free Trade Agreement and other multilateral pacts that Trump has vilified and sought to scrap or alter.

Besides trade, the two-day G-20 meeting highlights several other fissures between Trump and European leaders, including on climate change and immigration.

As protesters clashed with police armed with pepper stray and water cannons outside the summit Thursday, Trump and Merkel met directly for about an hour, according to German officials, who characterized the meeting as friendly but contentious, particularly on trade.

“The question is whether the Americans are still convinced that world trade always needs to be assessed according to one question, namely whether the U.S. is the winner, or whether we’ll manage to convince the Americans that when everyone plays by the same fair rules, everyone will be better off,” German Foreign Minister Sigmar Gabriel told German broadcaster ARD afterward.

The stop in Poland – which Trump called “the geographic heart of Europe” – was both a symbolic and strategic choice for the new American president. The Eastern European nation is a critical U.S. ally and perhaps the European capital most welcoming to Trump’s nationalist message.

Leaving little to chance at a tightly choreographed speech, Polish government officials arranged for buses to bring supporters into the city from the rural parts of the country, where the ruling party’s support is strongest.

Poland is one of the few NATO countries that has met an agreement to contribute at least 2 percent of its gross domestic product to defense spending, an issue that Trump has repeatedly raised since the campaign. It was one of many things Trump praised Poland for Thursday.

But Trump also said military spending alone is not enough to preserve Western civilization.

“Our own fight for the West does not begin on the battlefield,” he said. “It begins with our minds, our wills and our souls. Today, the ties that unite our civilization are no less vital and demand no less defense than that bare shred of land on which the hope of Poland once totally rested.”

POLAND A NATURAL ALLY

Speaking with nationalist overtones, he praised Poland as an example of a nation that had persevered despite grave challenges, saying it offered “the story of a people who have never lost hope, who have never been broken, and who have never forgotten who they are.”

Poland’s current right-leaning, populist government has proven a natural ally for Trump. The country’s Law and Justice Party has embraced some of the main pillars of Trump’s candidacy, including a similar resistance to accepting Muslim refugees.

“While we will always welcome new citizens who share our values and love our people, our borders will always be closed to terrorism and extremism,” Trump said Thursday. He also decried “the steady creep of government bureaucracy that drains the vitality and wealth of the people.”