When U.S. President Donald Trump spoke to the United Nations General Assembly yesterday, he deliberately signaled a definitive break with the internationalist consensus that has guided U.S. grand strategy since World War II. “We will never surrender America’s sovereignty to an unelected, unaccountable global bureaucracy,” he proclaimed. “Sovereign and independent nations are the only vehicle where freedom has ever survived, democracy has ever endured, or peace has ever prospered. And so we must protect our sovereignty and our cherished independence above all.” He was dumping cold war water on multilateralism and global governance—and the commentary that followed duly noted just how sharply his message diverged from those of his predecessors.

But Trump’s brand of statecraft is not in fact out of step with much of U.S. history. Rather, he is discarding the key tenets of U.S. foreign policy since World War II in favor of an older strain of thinking about the United States’ role in the world. As I argued in the March/April 2018 issue of this magazine (“The Clash of Exceptionalisms

Since Trump is not known for the depth and breadth of his historical knowledge, he is most likely not basing his foreign policy on a close reading of the United States’ past. But he does seem to have an uncanny ability to play to a heartland base that feels disadvantaged by globalization, immigration, and an expansive conception of international obligations—and which therefore yearns for the United States of yesteryear.

In his speech before the General Assembly, Trump attacked the multilateralism of the postwar era and emphasized that his top priority is to reclaim national sovereignty. He went on to aim one salvo after another at international institutions, including the International Criminal Court, the Global Compact for Migration, and the United Nations Human Rights Council. In his speech to the same body last year, his theme was the same: he repeatedly called for a world of “strong, sovereign nations,” each striving to put itself first.

Trump has backed this rhetoric with action. He has pulled out of one pact after another, from the Paris agreement to the Iran nuclear deal. He has appointed a national security adviser, John Bolton, well-known for his hostility to compacts that infringe on U.S. sovereignty. Trump is hostile even to institutions of which the United States is not a member: he supports the United Kingdom’s withdrawal from the European Union and aligns himself with populist governments in Italy, Poland, and Hungary that are hostile to the project of European integration.

Trump’s unilateralism is a sharp break with most of the recent past, but that doesn’t make it new.  ...