President Trump’s decision to make John Bolton his new national security adviser ricocheted around the globe Friday, unsettling allies and raising alarm that a hawk who advocates military action against North Korea and Iran will have the president’s ear.

From Berlin and Jerusalem to Seoul and Tokyo, U.S. allies who have been relieved that Trump’s unconventional rhetoric on foreign policy often has not translated to concrete policy are bracing for a shift. Following the nomination last week of the hawkish Mike Pompeo to become secretary of state, Bolton’s elevation means that Defense Secretary Jim Mattis is the lone survivor among a trifecta of advisers who pushed Trump to hew closer to conventional foreign policy positions.

Now, Bolton’s regime-change rhetoric toward North Korea and Iran may lead to a hardening of policy, allies believe. Europeans, who widely support a 2015 deal to restrict Iran’s nuclear program, fear its imminent demise. Some Israelis — even those who criticized the pact — are also concerned. And in South Korea and Japan, there are fears that Trump is preparing for war if talks with North Korean leader Kim Jong Un, expected by May, fail to yield breakthroughs.

More broadly, the appointment has fueled worries that the Trump administration is turning its back on Washington’s decades-long role as the preeminent guarantor of global stability.

“We would desperately wish to see the United States in a constructive leading role as a steward of the international system,” said Norbert Röttgen, chairman of the foreign affairs committee of the lower house of the German Parliament. He said he fears Washington is moving in the opposite direction.

“We are concerned that the policy is coming closer to the rhetoric,” he said. Trump “has now surrounded himself with people who share his intuitions and his general views.”

Some leaders dreaded increased turmoil.

“We are at the greatest risk of real conflict that we have been for many years, perhaps decades,” said Xenia Wickett, head of the Americas program at Chatham House, a London think tank.

The appointment inflamed concerns about the prospects of a conflict with North Korea. H.R. McMaster, the outgoing national security adviser, was no dove on Pyongyang, repeatedly talking about military options to make it give up its nuclear weapons program. But Bolton, who has advocated preemptive strikes, moves into the president’s inner circle as the South Korean president prepares to hold a summit with Kim Jong Un at the end of April, with Trump following suit in May.

“Trump is sending a message to the regime, telling them that they should come out to talks in order to avoid such drastic military backlash,” said Kim Sung-han, a former South Korean vice foreign minister who is now dean of Korea University’s Graduate School of International Studies.

Bolton has advocated a hard line against North Korea since he served as undersecretary of state for arms control and ambassador to the United Nations during the George W. Bush administration.

At that time, the North’s state-run Korean Central News Agency regularly denounced him, calling him “human scum and a bloodsucker.”

Bolton’s ascent raises the stakes of the diplomatic effort now underway.

Many national security analysts say the type of strike he has argued for would put the greater Seoul region, home to 25 million South Koreans, at risk of a counterstrike. Japan has also been increasingly concerned about becoming collateral damage, as North Korea last year fired several missiles over Japanese territory and threatened to strike American military bases in Japan.

“I am particularly worried that if the Trump-Kim summit fails, Bolton will take that as proof that we must hit North Korea,” said Robert Kelly, an American who teaches international relations at Pusan National University in South Korea.

In Europe, even before the Bolton move, leaders were gathered for a two-day summit in Brussels that was dominated by concerns about Trump’s tariffs on steel and aluminum, another area that threatens the transatlantic relationship that has underpinned Western stability since the end of the Cold War.

For Europeans, Bolton is a throwback to the era of clashes with Washington at the outset of the war in Iraq in 2003. This time, though, he will have far more power than in his Bush-era role.

“This is a person who guarantees allies will be driven away, allies will be insulted, allies will be ignored,” said Reinhard Bütikofer, a German member of the European Parliament. “It may have been forgotten a year into the Trump presidency, but it used to be kind of common sense that in a dangerous world, alliances are what make us strong.”

The appointment comes days after E.U. and U.S. officials clashed over the future of the Iran nuclear deal, which Europeans are trying desperately to preserve ahead of a key deadline for U.S. adherence to the pact.

The Trump administration has said it will not sign a new sanctions waiver for Iran by May 12 unless changes are made to the agreement on grounds that Tehran has not lived up to the “spirit” of the deal. Bolton has been a critic of the accord, which Europeans see as critical to avoiding war in their immediate neighborhood.

Before the appointment, optimism had been growing in Europe that Washington could be talked into some sort of compromise. Now the shifting currents have some here throwing up their hands, frustrated at yet another likely policy shift from their most important partner.

“With the appointment of Mike Pompeo on the one side, and John Bolton on the other, the group of personalities who have never made any mystery of their opposition to the nuclear deal with Iran is growing,” said Pierre Vimont, a retired senior French diplomat who has been involved in past negotiations with Iran.

The official response from Iranian officials was muted Friday.

The spokesman of the Guardian Council, a body of influential clerics, criticized Bolton as a supporter of the Mujahideen-e Khalq, an exile group that advocates the overthrow of the Islamic republic.

And an adviser to the speaker of parliament said that Trump had chosen Bolton as part of a more militarized approach to the Middle East. Hossein Amir-Abdollahian said that the United States only understands the “language of power” and that Iran’s military arsenal is essential to communicating that message.

In Israel, where many are critical of the Iran deal, Bolton’s appointment was widely welcomed by members of Prime Minister Benjamin Netanyahu’s right-wing government. Education Minister Naftali Bennett called Bolton an “extraordinary security expert, experienced diplomat and a stalwart friend of Israel.”

But even in Jerusalem, his return stirred some concern.

While Netanyahu has lobbied for the United States to “fix or nix” the Iran nuclear deal, some Israeli security officials have warned against a complete collapse of the pact — a prospect that may be more likely with Bolton as national security adviser. They argue that a flawed agreement is better than none at all. Bolton has said that the deal was a “strategic mistake” and should be “abrogated.” 

Meanwhile, Israel is likely to be at the sharp end of any conflict with Iran, something Bolton has repeatedly floated.

The Israeli security establishment is split, said Ofer Zalzberg, an analyst with the International Crisis Group. “There is a concern that he’s primarily an ideologue and there’s a risk to stability, and others who say he has decades of experience.”

Bolton’s ascension further infuriated Palestinians already angered by the U.S. Embassy’s planned move to Jerusalem.

The appointment of Bolton, who has argued that the Palestinians do not have a right to self-determination, “adds insult to injury,” said Hanan Ashrawi, a member of the Palestine Liberation Organization’s executive committee.

“This is unprecedented, this lethal combination of hard-liners, Israel-firsters, who are in charge of decision-making in the U.S.” 

Fifield reported from Tokyo and Morris from Jerusalem. Min Joo Kim in Seoul, Erin Cunningham in Istanbul and Ruth Eglash in Jerusalem contributed to this report.