LONDON — History was not supposed to turn out this way.

In the aftermath of World War II, the victorious Western countries forged institutions — NATO, the European Union, and the World Trade Organization — that aimed to keep the peace through collective military might and shared prosperity. They promoted democratic ideals and international trade while investing in the notion that coalitions were the antidote to destructive nationalism.

But now the model that has dominated geopolitical affairs for more than 70 years appears increasingly fragile. Its tenets are being challenged by a surge of nationalism and its institutions under assault from some of the very powers that constructed them — not least, the United States under President Trump.

In place of shared approaches to societal problems — from trade disputes, to security, to climate change — national interests have captured primacy. The language of multilateral cooperation has been drowned out by angry appeals to tribal solidarity, tendencies that are heightened by economic anxieties.

“What we’ve seen is a kind of backlash to liberal democracy,” said Amandine Crespy, a political scientist at Free University Brussels (ULB) in Belgium. “Masses of people feel they have not been properly represented in liberal democracy.”