They promised a harder line against China.

They assailed President Biden’s withdrawal from Afghanistan.

They attributed the conflicts in Ukraine and Israel to American weakness, pledged a crackdown on undocumented immigrants and vowed to end “free rides” for American allies.

The lineup of speakers at the Republican National Convention on Wednesday sketched out a vision for American foreign policy that leans harder into former President Donald J. Trump’s populist and isolationist instincts and further jettisons long-held Republican views.

The rest of the world was watching.

For months, officials around the globe have weighed the possibility of Mr. Trump’s return to the White House. In Buenos Aires, Riyadh and Budapest, leaders could be expected to welcome it. In London, Seoul and Berlin, it would likely further test faith in American dependability. And in Mexico City, Kyiv and Beijing, leaders appear to be steeling themselves for potential upheaval and further ruptures.

Already, with Mr. Trump consistently polling ahead of Mr. Biden, some governments are taking concrete steps to prepare for the former president’s possible return.

South Korea is racing to finalize a deal with Washington on sharing the costs of keeping U.S. troops in the country, anticipating Mr. Trump will demand that Seoul pay more. Mexico is studying how to protect millions of its citizens who might be deported from the United States.

In Ukraine, leaders are trying to remain as neutral as possible in the U.S. presidential campaign, while also shoring up support from other Western allies.

Europe put on a show of solidarity at a summit of more than 40 European leaders on Thursday, hosted by the new U.K. Prime Minister Keir Starmer at a palace outside Oxford. There, President Volodymyr Zelensky of Ukraine said that Russia had “failed to create division in Europe” and appealed for more air defenses and fewer restrictions on Western weapons.

Mr. Zelensky’s government is simultaneously trying to build bridges with Mr. Trump’s camp. “If Mr. Donald Trump becomes president, then we will work with him,” Mr. Zelensky said in Kyiv on Monday. “I am not afraid of it.”

Mr. Trump’s allies overseas are feeling more confident about their global influence. Viktor Orban, the prime minister of Hungary and Mr. Trump’s staunchest ally in Europe, shuttled to Kyiv, Moscow, Beijing and Washington in recent weeks, fashioning himself as a self-appointed global diplomat on the war in Ukraine. He concluded his travels with an audience with Mr. Trump at Mar-a-Lago.

And those from nations who have faced Mr. Trump’s attacks are already on the defensive.

President Andrés Manuel López Obrador of Mexico criticized the Republican convention speakers for blaming American problems on Latin American migrants. He noted on Wednesday that American officials were ignoring the serious problem of drug use among young people.

“Let them look for an answer to that instead of only looking toward the south,” he said.

The speakers at the Republican National Convention on Wednesday emphasized American support for Israel, but made little mention of Ukraine, an issue that has divided the party. That mixed approach mirrored the party platform released earlier this month, in which Republicans backed Israel by name, but omitted the words “democracy” or “Ukraine.”

Benjamin Netanyahu, the Israeli prime minister, angered Mr. Trump by congratulating Mr. Biden after the presidential election in 2020 — a move that Mr. Trump considered disloyal and strained their relationship.

But the pair had strong ties during the first Trump presidency and the possibility of Mr. Trump’s return was expected to benefit Mr. Netanyahu’s right-wing government, particularly if the war in Gaza were to extend into next year.

During his first term, Mr. Trump moved the U.S. embassy to Jerusalem and was an architect of the landmark deals that forged formal diplomatic ties between Israel and three Arab states. If he wins, he is expected to press ahead with Mr. Biden’s efforts to forge a similar arrangement between Israel and Saudi Arabia.

Unpredictability

Across the spectrum, foreign analysts and officials have underscored the unpredictability that defined Mr. Trump’s first term. Some nations point out that Mr. Trump doesn’t always follow through on his public threats.

“He may say something publicly and act differently when he’s in power,” said Sergiy Solodkyy, the first deputy director of the New Europe Center, a think tank in Ukraine.

Mr. Trump, for example, muted his opposition to American aid to Ukraine earlier this year, enabling some Republican members of Congress to vote in favor of the military package after months of stalling, Mr. Solodkyy said.

“Trump is a politician who can change his mind,” he added.

The unpredictability cuts both ways. In Moscow, Russian officials rejoiced when Mr. Trump won the presidency, only to find an administration packed with hawkish, anti-Russia Republicans, who pushed through new rounds of Russian sanctions, lethal aid to Ukraine and withdrawals from arms control pacts, at times over Mr. Trump’s protests.

President Vladimir V. Putin of Russia said earlier this year he would prefer a victory for Mr. Biden, citing the president’s experience and predictable behavior. But some analysts who follow the Kremlin suggested an ulterior motive in Mr. Putin’s comments, with the Russian leader knowing that his endorsement would hurt any candidate among American voters.

Global leaders needed to look no further than Mr. Trump’s choice of a running mate, Ohio Senator J.D. Vance, to see how foreign policy in Mr. Trump’s second term might shift.

Mr. Vance has positioned himself as the standard-bearer of a fully Trump-aligned foreign policy, in contrast to the more traditional G.O.P. positions held by Mr. Trump’s earlier running mate, Mike Pence.

Mr. Vance led the charge against additional aid to Ukraine in the Senate early this year, and pro-Kremlin commentators in Moscow embraced his nomination this week as Mr. Trump’s running mate.

During a speech at the convention on Wednesday, Mr. Vance warned U.S. military allies that there would be “no more free rides.” And he took aim at China, vowing to “stop the Chinese Communist Party from building their middle class on the backs of our hard-working citizens.”

Mr. Vance supports strong American backing for Taiwan, but Mr. Trump himself has expressed skepticism about the semiautonomous Chinese territory’s effort to defend itself. He has also accused Taiwan of luring semiconductor production away from the United States.

Foreign policy experts in China expect a possible second Trump administration to look much like the first, with friction increasing between Beijing and Washington, particularly on economic issues. But the Biden administration has also taken a hawkish stance on China.

Personality-Driven Policy

Even as they assess Republican ideology, analysts in Asia have noted the significance of the former president’s outsize personality.

During Mr. Trump’s presidency, Shinzo Abe, the former prime minister of Japan, was particularly adept at developing a close personal relationship with the American leader. Mr. Abe, who was assassinated in 2022, figured out how to flatter Mr. Trump to sidestep direct confrontations over demands that Japan pay more for defense.

“There will almost be a playbook on how to deal with Trump and a lot to learn from Abe’s successes — that really, sycophancy works,” said James D.J. Brown, a professor of political science at the Tokyo campus of Temple University.

Across the globe, that approach is already underway.

In the United Arab Emirates, pro-government pundits and businessmen have been open in their praise for Mr. Trump recently.

Saudi Arabia would also likely welcome Mr. Trump’s return. Two weeks ago, the Trump Organization signed a deal with a real estate company in Saudi Arabia to build a residential high-rise tower there, extending the family’s close ties with the kingdom.

During his presidency, Mr. Trump had particularly warm relations with Saudi Crown Prince Mohammed bin Salman, defending him after the 2018 murder of Washington Post columnist Jamal Khashoggi by Saudi agents in Istanbul.

“I know him very well, he’s a great guy,” Mr. Trump said of the Saudi Crown Prince in an interview with Bloomberg published this week.

Renewed Tension in Latin America

Though Argentina’s right-wing president, Javier Milei, has told Mr. Trump personally that he wants him to win, elsewhere in Latin America, diplomatic turmoil is expected, with leftist governments in Mexico, Brazil and Colombia poised to disagree with Mr. Trump’s policies.

Mexico is preparing to offer alternatives to the kinds of harsh border measures Republicans have promised to introduce, including “Remain in Mexico,” a policy that requires migrants to wait in the country in sprawling tent encampments along the border while they apply for asylum in the United States.

In Brazil, President Luiz Inácio Lula da Silva has repeatedly criticized Mr. Trump publicly and supported Mr. Biden, expressing an affinity for the U.S. president after the two men found common ground on their shared experiences as the targets of far-right, election deniers. Yet despite that friendship, Mr. Lula has criticized U.S. foreign policy, including on Ukraine, Israel and Venezuela.

Analysts believe that a Trump presidency would likely push Brazil away from the United States and closer to China, at least under Mr. Lula. They predict a similar dynamic in Colombia, one of Washington’s most important allies, which has a leftist president for the first time, known for being a prolific communicator on social media.

Motoko Rich, Keith Bradsher, Julie Turkewitz, Natalie Kitroeff, Jack Nicas, Constant Meheut, Vivian Nereim, Patrick Kingsley, Anupreeta Das, Chris Buckley, Pragati K.B., Stephen Castle and Lauren Katzenberg contributed reporting.

French lawmakers prepared to elect the president of the National Assembly on Thursday, in a vote seen as a test of the power balances between the country’s political forces and as a potential indicator of the direction any new government would take.

The gathering of the Assembly, the lower house of Parliament, was its first since no party gained an outright majority in the second round of a snap election on July 7. It was unclear which political force the new president of the Assembly would emerge from.

The president of the National Assembly does not have executive powers, but this election could mark the emergence of a majority, even if not an absolute one, that could weigh on President Emmanuel Macron’s choice of the next prime minister.

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