WASHINGTON — The trend emerged into public consciousness last year with the rise of far-right politics in Europe. It spread with Donald J. Trump’s successful campaign to become the presumptive Republican presidential nominee in the United States. And its consequences became unmistakable with Britain’s vote last month to exit the European Union.

What is driving this surge in anti-immigrant populism in Western politics?

Michael Ignatieff has a theory, one rooted in his research as a professor at the Kennedy School of Government at Harvard, and in his experience as former leader of Canada’s Liberal Party.

According to his argument, what we’re seeing is, in part, an ideological split between cosmopolitan elites who see immigration as a common good based in universal rights, and voters who see it as a gift conferred on certain outsiders deemed worthy of joining the community.

This disagreement, he said in an interview, has animated much of the backlash against immigration that is described as “uncontrolled” and a threat to receiving communities. These disagreements over “who belongs,” he said, will “define the 21st century.”