The greatest threat to American security is something most Americans never think of. President Barack Obama touched on it in his speech to the European people a week ago in Germany.

I’m not referring to the Islamic State, although Obama called the terrorist group “the most urgent threat to our nations” in his remarks. I’m talking about a more existential threat to Europe (and America): a diminishing faith in democracy as a political system.

On the continent, this is manifested by the widening cracks in the European Union and the rise of radical right-wing parties.

“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,” Obama said, this will have a negative impact worldwide.

“We will be empowering those who argue that democracy can’t work, that intolerance and tribalism and organizing ourselves along ethnic lines, and authoritarianism and restrictions on the press — that those are things that the challenges of today demand.”

The president’s tone was a stark reflection of how much the world has changed since candidate Obama gave his famous speech in front of tens of thousands of cheering Berliners in 2008. Back then, he proclaimed “this is our moment” to “remake the world again” in partnership with Russia, with a “new dawn” in the Mideast, in pursuit of an end to terrorism and a world without nuclear weapons.

That was then.

Yet irrespective of Obama’s policies, the global shifts since 2008 were bound to stress Europe’s democratic institutions — and undermine European unity. Globalization, the demise of manufacturing economies, and the 2008 crash (which Europeans blame on the George W. Bush administration) all contributed to a faltering European economy that has yet to recover. The EU’s Brussels bureaucracy and institutions often seem incapable of coping with current realities.

The U.S. invasion of Iraq, combined with the failure of the Arab Spring and the incompetence of Mideast leaders, plus an enormous Arab youth bulge, created a flow of desperate young immigrants headed for Europe. This fueled the rise of the Islamic State.

As Obama noted, German Chancellor Angela Merkel appealed to Europe’s best instincts and values when she welcomed the flood of refugees seeking asylum from the violence in Syria and Afghanistan. But her humanitarian instincts — born of a postwar German sensitivity to the issue of refugees — backfired. Her generosity crashed into a growing public fear of terrorists posing as asylum seekers.

The refugees also provided a convenient scapegoat for European angst. Right-wing populist parties in several countries — some funded by Russia — used the immigration issue as a club to oppose Merkel, the European Union, and NATO.

Their efforts were enhanced by a widening European memory gap. Three generations of Western Europeans have come of age since World War II, and only the aged can recall the earlier years of the 20th century, when European disunity produced wars and vicious totalitarian regimes. As for much of Eastern Europe, the two and a half decades since the fall of the Berlin Wall haven’t fully erased the deep hold that authoritarian communist rule exercised over instincts and institutions.

So the value of European unity may seem far less apparent to many Europeans today than it did to previous generations.

Add all this up, and you have a deeply uncertain Europe, many of its citizens skeptical about unity, dissatisfied with democracy, and too often turning inward toward ethnic separation and intolerance of others.

In his speech, Obama tried to be upbeat. But the president admitted he might be relying on “blind hope,” and there was a plaintive note to his entreaties. Any U.S. plea for European unity and democracy is undercut by an American election campaign in which the presumptive GOP candidate, Donald Trump, promotes intolerance at home and calls Merkel “insane.”

Trump suggests NATO is unnecessary and lauds Russia’s Vladimir Putin. Recall that Putin is touting his version of authoritarian “democracy” as superior to the Western brand — with himself as the leader of the new movement.

His claim has been warmly received by some of Europe’s populist parties.

Indeed, the results of the U.S. election may well play into the struggle for the future of Europe. In Germany, Obama was pleading for Europe to stay united and democratic, but his warning is equally applicable to the United States.

Trudy Rubin writes for the Philadelphia Inquirer.