UNITED NATIONS — President Trump brought the same confrontational style of leadership he has used at home to the world’s most prominent stage on Tuesday as he vowed to “totally destroy North Korea” if it threatened the United States and denounced the nuclear agreement with Iran as “an embarrassment” that he may abandon.
In his first address to the United Nations General Assembly, Mr. Trump framed the conflicts as a test of the international system. The bombastic flourishes that generate approving roars at political events were met by stony silence, interrupted a few times by a smattering of applause, as Mr. Trump promised to “crush loser terrorists,” mocked North Korea’s leader as “Rocket Man” and declared that parts of the world “are going to hell.”
The president’s tone carried real-world implications for the future of the United Nations and the escalating confrontations with international outliers. In the space of 42 minutes, he upended decades of rhetorical support by the United States for the collective philosophy of the United Nations as he defended his America First policy. He repeatedly extolled “sovereignty” in a setting where the term traditionally has been brandished by nations like Russia, China, Iran and North Korea to deflect criticism.
“As president of the United States, I will always put America first, just like you, as the leaders of your countries, will always and should always put your countries first,” he said, generating light applause in parts of the chamber. But he argued that nationalism can be the foundation for strong nations to join common causes.
“If the righteous many do not confront the wicked few, then evil will triumph,” he said. “When decent people and nations become bystanders to history, the forces of destruction only gather power and strength.”
Mr. Trump singled out North Korea, broadening his indictment of the Pyongyang government beyond its pursuit of nuclear weapons to its treatment of its own people and captured foreigners like the American college student who died shortly after being sent back to the United States.
“No nation on Earth has an interest in seeing this band of criminals arm itself with nuclear weapons and missiles,” Mr. Trump said. “The United States has great strength and patience, but if it is forced to defend itself or its allies, we will have no choice but to totally destroy North Korea. Rocket Man is on a suicide mission for himself and for his regime.”
Without mentioning it by name, Mr. Trump also chastised China for continuing to deal with its rogue neighbor, calling it “an outrage that some nations” would trade, arm and support North Korea.
He assailed the Iran agreement, which was negotiated by President Barack Obama and leaders of five other powers and ratified by the United Nations Security Council to curb Tehran’s nuclear program for a decade in exchange for lifting international sanctions. Under American law, Mr. Trump has until Oct. 15 to certify whether Iran is complying with the agreement, which he has done twice so far since taking office. But he has made clear that he would prefer not to do so again, which could unravel the accord.
“The Iran deal was one of the worst and most one-sided transactions the United States has ever entered into,” Mr. Trump said. “Frankly, that deal is an embarrassment to the United States, and I don’t think you’ve heard the last of it, believe me.”
The tough words cheered the delegation from Israel, whose prime minister, Benjamin Netanyahu, applauded from the gallery and called it the boldest speech he had heard at the United Nations in 30 years. In his own address later, he said Mr. Trump had “rightly called the nuclear deal with Iran an embarrassment” and pointed to North Korea as an example.
“In the last few months, we’ve all seen how dangerous even a few nuclear weapons can be in the hands of a small rogue regime,” Mr. Netanyahu said. “Now imagine the danger of hundreds of nuclear weapons in the reins of a vast Iranian empire, with the missiles to deliver them anywhere on earth.”
Others called Mr. Trump’s speech excessively belligerent. “If Trump was determined to demonstrate to the world that he is unhinged and an imminent danger to world peace, he has succeeded with this speech, and will only make it harder for him to win over the world to his self-destructive goals,” said Trita Parsi, president of the National Iranian American Council, a Washington-based group that criticizes the Tehran government but advocates more engagement.
Neither Hassan Rouhani, Iran’s president, nor Mohammad Javad Zarif, its foreign minister, was in the hall for Mr. Trump’s speech. North Korea’s ambassador left his seat before the president started speaking.
In an interview taped before the speech, Mr. Rouhani castigated Mr. Trump for considering a withdrawal from the nuclear accord. “The exiting of the United States from such an agreement would carry a high cost, meaning that subsequent to such an action by the United States of America, no one will trust America again,” he told NBC News.
Mr. Trump’s choice of words raised hackles among allies too, as Federica Mogherini, the European Union foreign minister, made clear at a reception on Tuesday evening. “We never talk about destroying countries,” she said.
President Emmanuel Macron of France, who has a friendly relationship with Mr. Trump and whose country was one of the negotiating parties for the Iran deal, likewise took exception. In his General Assembly address, Mr. Macron called the agreement “solid, robust and verifiable,” and said renouncing it would be a “grave error.”
While he shared Mr. Trump’s view that North Korea’s nuclear belligerence was dangerous and unacceptable, Mr. Macron said multilateral diplomatic pressure was the best solution. “France rejects escalation and will not close any door to dialogue,” he said.
The French president also confronted a big issue Mr. Trump conspicuously omitted, climate change. “The planet will not negotiate with us,” Mr. Macron said, referring to the Paris climate accord that Mr. Trump has renounced.
The United Nations secretary general, António Guterres, likewise implicitly rebuffed Mr. Trump on climate change. “We know enough today to act,” he said as he opened the General Assembly session. “The science is unassailable.”
The early reaction from China was relatively mild, perhaps a reflection of Mr. Trump’s phone call to President Xi Jinping the night before. In an editorial on Wednesday, the state-run China Daily scolded the United States for not doing more to start talks with North Korea. “His threat to ‘totally destroy’ the D.P.R.K. if need be will, therefore, likely worsen the already volatile situation,” the paper said, using an acronym for North Korea.
Republican lawmakers and conservative leaders cheered the president’s strong stance against international outliers like Iran and North Korea.
“It was the best speech of the Trump presidency in my view,” John R. Bolton, a former ambassador to the United Nations, told Fox News. “It’s safe to say in the entire history of the United Nations there has never been a more straightforward criticism of the behavior, the unacceptable behavior of other member states.”
Mr. Trump arrived at the United Nations with a more overtly nationalist approach than past American presidents, predicated on a belief that the United States has been taken advantage of in areas like trade, security and other international affairs. In addition to abandoning the Paris accord, he has renounced the Trans-Pacific Partnership trade pact and threatened to scrap the North American Free Trade Agreement if it is not renegotiated to his liking.
In his speech, he used the word “sovereign” or “sovereignty” 21 times. “The United States will forever be a great friend to the world, and especially to its allies,” he said. “But we can no longer be taken advantage of, or enter into a one-sided deal where the United States gets nothing in return.”
Mr. Trump mentioned only in passing one of the most prominent examples of a violation of sovereignty in recent years, the still-unresolved Russian intervention in Ukraine and annexation of Crimea. But he went on to denounce the actions of Venezuela’s government against its own people without explaining how that fit into his concept of respecting sovereignty.
“The Socialist dictatorship of Nicolás Maduro has inflicted terrible pain and suffering on the good people of that country,” Mr. Trump said. “This corrupt regime destroyed a prosperous nation by imposing a failed ideology that has produced poverty and misery everywhere it has been tried.”
Still, he avoided some of the harsh language he has used in the past about the United Nations itself. “For years, I’ve been a critic,” he said in a toast at a luncheon given by Mr. Guterres, “but I’ve also been somebody that said the United Nations has tremendous potential.”
The president met separately with Sheikh Tamim bin Hamad al-Thani, the emir of Qatar, a Persian Gulf state Mr. Trump has accused of being a “funder of terrorism.” He eschewed such characterizations on Tuesday, instead calling the emir a longtime friend and renewing his offer to mediate a standoff between Qatar and other Arab countries.
“We are right now in a situation where we’re trying to solve a problem in the Middle East and I think we’ll get it solved,” Mr. Trump said. “I have a very strong feeling that it will be solved pretty quickly.”
The emir welcomed his help. “As you said, Mr. President, we have a problem with our neighbors and your interference will help a lot and I’m sure we can find a solution for this problem,” he said.