A section of the U.S.-Mexico border wall near the Mexican city of Ciudad JuarezJose Luis Gonzalez / Reuters

Donald Trump ended his journey to the American presidency the way he began it: by vowing to restore the borders of the United States. In launching his campaign a year and a half ago, Trump promised a wall to keep out Mexican immigrants and tariffs to keep out foreign-made cars. After taking his oath of office on Friday, Trump essentially announced what amounts to a dramatic break with decades of American foreign policy: The U.S. government will no longer focus on sustaining peace and prosperity beyond its borders.

“A nation exists to serve its citizens,” not those of other countries, Trump declared. He issued a “new decree to be heard in every city, in every foreign capital, and in every hall of power”—that U.S. decisions related to trade, immigration, and foreign affairs would “be made to benefit American workers and American families.”

“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 nations’ borders while refusing to defend our own.”

Many Republicans and Democrats support the things Trump is criticizing—free trade, U.S. military alliances, the numerous other border-transcending aspects of globalization—but not because they want to serve people in other countries more than their own people. Rather, it’s because they feel these things prevent major military conflicts and promote economic growth, openness, and interdependency in ways that ultimately benefit American workers and families. These benefits aren’t always apparent; you don’t, for example, notice a world war that never happens.

Trump, however, thinks these arguments are nonsense. He argues that America’s embrace of “globalism” has only stripped the country of its wealth, power, and ability to control its own affairs. As he once put it, the “nation-state remains the true foundation of peace and harmony.”

In this way, Trump has emerged as the most prominent spokesman for a brand of nationalism that is gaining ground in many countries. Border walls and fences are going up around the world at an accelerating pace. Populist, anti-globalization political parties are growing more popular in Europe as rates of immigration increase. “At least since Genghis Khan secured travel along the Silk Road, the flow of goods, money and people across borders has advanced and retreated in decades-long waves,” Ruchir Sharma wrote this fall in The New York Times. “The retreat that began in 1914 continued for three decades, weakening the world economy and feeding the resentments that erupted into World War II. The retreat that began in 2008 is still gaining strength.”

In a recent study of how the concept of borders has changed over the last 500 years, the historian Charles Maier makes a critical distinction regarding territory that can be applied to Trump’s inaugural message. Territory is an “identity space,” he notes, providing a sense of belonging just like a person’s race or religion might. “Territory is still the emotional reference point for legal belonging,” Maier writes. But territory has also long served as a “decision space,” establishing the “reach of legislation and collective decisions” about “who belonged and who was foreign, how wealth would be generated and distributed, how the domain of the sacred must be honored, how families reproduced themselves.”

Globalization, Maier argues, has proven so disruptive and divisive because it has weakened decision space but not identity space. Nationalism remains strong, even as national leaders struggle to control what happens within their countries:

Through the first three quarters of the twentieth century, excepting experiences of wartime or emigration, most adults in the West understood their decision space and their identity space to be congruent. The areas that claimed their loyalty also organized their labor, provided security, and ensured family continuity. Today these domains no longer coincide so pervasively. Territoriality seems less a resource for guaranteeing livelihoods, excluding foreigners, or maintaining coherence of values. It no longer provides the same capacity for control, even if territories remain the nexus of primary allegiance. Identity space and decision space have diverged.

Globalization, Maier notes, has divided politicians into “globalists,” who “believe in and benefit from the new flows of capital and employment,” and “territorialists,” who “fear that their jobs and traditional values are being sacrificed.” These camps cut across traditional party lines, which is scrambling the way politics works in many countries. Donald Trump, for example, favors policies of the “territorialist Left,” including the imposition of trade barriers to protect jobs, and policies of the “territorialist Right,” such as fortifying borders to prevent migration.

On Friday, Trump called not just for the government to solely consider Americans when making its decisions, but also for Americans to display “total allegiance to the United States of America.” In a sense, he called for America’s decision space and identity space to be reunited. In an era of globalization, that could bring about profound change.

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