In the run-up to Memorial Day, the commemoration of the fallen from America’s wars, Donald Trump put the world on notice that he is prepared to fight another one. He issued the warning two hours after cancelling his summit with North Korea, and in consultation with the Pentagon. “I’ve spoken to General Mattis and the Joint Chiefs of Staff, and our military—which is by far the most powerful anywhere in the world, and has been greatly enhanced recently, as you all know—is ready if necessary,” he said, in comments from the Roosevelt Room at the White House. “Hopefully, positive things will be taking place with respect to the future of North Korea, but if they don’t we are more ready than we have ever been before.”

Trump still wants a summit with Kim Jong Un, the White House insisted on Thursday. As Trump headed to his helicopter on Friday morning, he told reporters that discussions between Washington and Pyongyang had resumed. He even held out hope for the June 12th date in Singapore. But his words were the latest unsettling prospect in a tumultuous time of all-or-nothing diplomacy that intrinsically increases the dangers of conflict. In the fifteen months of Trump’s Presidency, the United State has witnessed a stunning undoing of long-standing norms—of the U.S.-led world order, core alliances, trade pacts, principles of nonproliferation, patterns of globalization, world institutions, and, most of all, U.S. influence. A lot of it began in 2003, with the U.S. invasion of Iraq. But it has accelerated with breathtaking speed since Trump took office.

And, in virtually every case, there is increasingly no alternative to replace the institutions, ideas, accords, and relationships that Trump is undoing.

“The world you are entering is one filled by a large number of uncertainties and threats,” Richard Haass, the president of the Council on Foreign Relations, said at Colgate University’s commencement last Sunday. “The quality and quantity of the challenges facing the United States and the world are unprecedented, in my experience.”

The litany is long: a rising China; Russia’s interference in several democratic elections and its forcible challenge of sovereign borders; North Korea’s unprecedented nuclear arsenal; Syria’s catastrophic civil war; Iran’s destabilizing interventions and the collapse of the nuclear deal; new turmoil along the Israeli-Palestinian border; the unravelling of global trade pacts; the dismemberment of the European Union; Venezuela’s breakdown; and America’s longest war, in Afghanistan.

“These are but a few of the challenges awaiting you,” Haass, who has worked for three Republican Presidents and in one Democratic Administration, said. “Hovering above them all is the fundamental question of whether the United States will continue to disrupt important elements of the world order it did so much to build and so much to maintain over the past seventy years.”

Trump has disrupted the global order far more than the domestic order, Ian Bremmer, the president of the Eurasia Group, told me. “Domestically, the President has not had a huge impact on policy. Everything has been resisted by the ‘swamp,’ the bureaucracy, and Congress,” he said. “Internationally, the world was already moving away from the U.S.-led order when Trump took office. But he is pushing a rock that was already rolling down the hill much faster.” In a commencement speech at the Naval Academy on Friday, Trump touted the success of an agenda that rejects past policies and promotes stand-alone U.S. supremacy in the world. “We are not going to apologize for America—we are going to stand up for America. No more apologies,” Trump said. “They are respecting us again. Yes, America is back.” He told cadets at the Annapolis stadium, “Winning is such a great feeling, isn’t it? Nothing like winning. You got to win.”

Every President has charted distinctive policies. Presidents George W. Bush and Barack Obama had starkly different views of the Iraq War, even as they both believed that the United States had to confront extremism and stabilize Iraq. But, in an approach that appears more instinctive than strategic, Trump has moved more aggressively in changing the world order than any previous President, Douglas Brinkley, a historian and Presidential biographer at Rice University, told me. He said that Trump has the style of Ronald Reagan but lacks the “spiritual sense.” “Trump leaves God out of his thinking. It’s a raw power crunch,” Brinkley, who has read Reagan’s diaries, said.

Trump’s “America First” ideology differs starkly even from that of isolationist Presidents, who still promoted democracy and the American model of government. In contrast, Trump has little interest in democracy-building—widely believed to be the greatest deterrent to war—and “admires dictators for their ability to consolidate power,” Brinkley said. “No President has done this.”

Like Richard Nixon, Trump also doesn’t trust the foreign-policy establishment at the State Department, at the National Security Council, or in the intelligence community, which has crafted diverse policies based on a consensus of principles since the Second World War. He has rejected “the group-speak of the past seventy years” and largely snubbed a community that had “treated him as a nobody” before he was elected, Brinkley said. Ignoring the experts, and with a limited sense of history, Trump has an approach to the world based on exclusive Presidential control and “blowing things up in a chaotic way,” he added.

Trump has challenged the global order by doing the same thing to long-standing allies. In his decision to cancel the North Korea summit, he spurned the closest U.S. allies in Asia—South Korea and Japan—with no advance consultation. The South Korean President, Moon Jae-in, had been in the Oval Office less than forty-eight hours beforehand. En route to Washington, his national-security adviser had told the accompanying press that he was “99.9 per cent” certain that the summit would happen.

After Trump aborted the summit, Moon held an emergency session with staff shortly before midnight on Thursday. A local news agency quoted Moon as saying, “I am very perplexed, and it is very regrettable.” The dismantling of North Korea’s nuclear program is a “historic” task “that can neither be abandoned nor delayed,” Moon said.

Trump used the same tact with European allies on the 2015 Iran deal, spurning personal interventions by the leaders of Britain, France, and Germany to work on compromise language to salvage the most significant nonproliferation treaty in more than a quarter century. They were party to two years of intense diplomacy and were co-sponsors of the deal, as were China and Russia. Shortly before rejecting the deal, the President issued a blunt warning. Iran “will pay a price like few countries have ever paid” in any showdown, he said.

“Trump has little interest in working with allies,” Bremmer told me. “He wrong-foots them all the time. He sees them as constraints.”

When it comes to allies on any continent, Trump wants to be more than first among equals, which is the traditional U.S. role. He employs one-upmanship and humiliation to claim position. In his meeting with President Emmanuel Macron, Trump made an embarrassing point of brushing dandruff off the French leader’s suit while television cameras were rolling. “And that’s the one world leader who was trying the hardest to understand him,” Brinkley said. Leaders now fear his personal and policy narcissism, he added.