BERLIN — U.S. President Donald Trump’s message to America’s allies in his inaugural address was as unmistakable as it was brutal: Don't count on us.

“For many decades, we've enriched foreign industry at the expense of American industry, subsidized the armies of other countries, while allowing for the very sad depletion of our military,” Trump said. “We've defended other nation's borders while refusing to defend our own. And spent trillions and trillions of dollars overseas, while America's infrastructure has fallen into disrepair and decay.”

If Trump’s intention was to put Europe on notice, he succeeded.

No region has benefited more from U.S. security guarantees since World War II than Europe. Washington’s unconditional commitment to defend the Continent, expressed in Article 5 of the NATO treaty, allowed Europe to outsource its security to the U.S. That paved the way for European integration by blunting the national rivalries that had underpinned centuries of conflict. The stability spawned a period of peace and prosperity unique in the Continent’s history. Along the way, the U.S. also benefited, both from its largely unfettered access to European markets and by leading a community of like-minded liberal democracies. Or so Europe thought.

Hostile inauguration speech. We can't sit around &hope for US support & cooperation.Europe must take its destiny & security in its own hands — Guy Verhofstadt (@GuyVerhofstadt) January 20, 2017

Even before the speech, those pillars of the Western world order appeared to be cracking. Trump’s recent references to NATO as “obsolete,” the blandishments he heaped on Russian President Vladimir Putin, not to mention his admission that he didn’t really care if the European Union survived, left the Continent on edge.

In recent weeks, American officials had tried to downplay Trump’s often bombastic pronouncements. “Don’t overreact to the tweets,” John Emerson, U.S. ambassador to Berlin, told an audience in a farewell speech this month. He noted that Trump had authorized President Barack Obama to reassure European allies during a November trip to the region that the U.S. would stick to NATO’s mutual defense guarantees during his presidency.

“The fundamentals are at stake” -- Jan Techau, Richard C. Holbrooke Forum director

Yet the inaugural speech raised fresh doubts about that commitment. Instead of trying to assuage allies’ concerns, Trump poured more oil on the fire.

“We assembled here today are issuing a new decree to be heard in every city, in every foreign capital, and in every hall of power,” he said. “From this day forward, a new vision will govern our land, from this day forward, it's going to be only America first. America first.”

In his roughly 15-minute-long speech, Trump mentioned neither NATO, nor the European Union, nor Europe. His only reference to allies came in passing: “We will reinforce old alliances and form new ones,” he said.

Europe’s biggest fear is that Trump plans to pursue a deal with Russia that could leave it in the cold. One theory is that Trump sees the U.S.’s foreign policy priorities in challenging China and destroying the so-called Islamic State. If Trump decides to enlist Putin in those quests, Europe could be left on the wayside, leaving it vulnerable to Russian threats. Countries could forge new alliances within the region, dividing the Continent once again.

“The fundamentals are at stake,” said Jan Techau, director of the Richard C. Holbrooke Forum in Berlin.

In a presentation at Berlin’s American Academy earlier this week, Techau sketched out a worst-case scenario for U.S. disengagement in Europe.

Should it become clear that the U.S.’s security guarantee for the Continent is no longer unconditional, NATO could collapse, he warned. That, in turn, could precipitate the dissolution of the EU and the euro.

“We have to prepare for the worst,” Techau said, though he stressed that such a doomsday scenario remained unlikely.

Nonethless, until Trump, such discussions would have been unthinkable in Europe. Despite transatlantic tensions about Iraq and the war on terror, few questioned the viability of the alliance.

For Europe, the U.S. was like an unmovable rock to which the Continent was tethered, said Thomas Bagger, the head of policy planning at the German foreign ministry.

“Now it’s drifting. We don’t know how far and they don’t know how far,” he said.

A crucial signal for Europe will be whether Trump meets first with Putin or with a European leader such as Angela Merkel. The German chancellor said this week she would welcome the opportunity to visit Trump in Washington but has yet to be invited.

Even if Washington reiterates its commitment to NATO in the coming weeks and months, Trump has so destabilized the equilibrium in the region that it may not matter. In other words, simply questioning the basic tenets of the security architecture sows doubts about the U.S. commitment that could take a long time to reverse.

“It’s a shock to the system,” said Vali Nasr, dean of the School of Advanced International Studies at Johns Hopkins, during an appearance in Berlin this week. “Even if you don’t go through with it, it has enormous impact.”