The timing appeared to be both calculated and opportunistic.

As soon as a deal to end fighting between Israel and Hezbollah in Lebanon was signed last week, another conflict kicked off not far away in Syria.

Syrian rebels launched sweeping assaults against the forces of President Bashar al-Assad in northwestern Syria, taking control of large portions of territory, including much of the city of Aleppo.

The rebels also forced Russian forces to abandon a base near Aleppo and militias backed by Iran to cede control of the town of Tel Rifaat, a Syrian outpost near the Turkish border, according to Syrian humanitarian and research groups.

The sudden advance of the rebels, and the setback for Mr. al-Assad and his allies, has stoked a cauldron of geopolitical rivalries that has simmered in Syria for more than a decade after a democracy uprising in 2011 turned into full-scale rebellion.

It has also underlined how easy it is for violence to spread like wildfire across a volatile region made all the more unpredictable by the intertwining and competing interests of numerous large powers vying for influence.

Iran and Russia, hoping to prop up a key ally in the region, have been providing vital military support to Mr. al-Assad’s government for years. Russian planes have bombed rebel positions, while on the ground, Iranian-backed militias like the Lebanon-based Hezbollah have battled rebel fighters in support of the Syrian government.

Turkey and the United States also have troops present in Syria in areas not controlled by the government where they support different rebel groups — Turkey in the northwestern region, and the United States in the northeast.

In the offensive that began last week, various Syrian rebel groups have united under the leadership of Hayat Tahrir al-Sham, a former affiliate of the terrorist group Al Qaeda. Hayat Tahrir al-Sham had been controlling most of the territory in northwestern Syria held by opposition groups.

The rebels had clearly seized an opportunity that presented itself with the Syrian government, Russia and Iran all weakened and overstretched by other conflicts, said Mouaz Moustafa, the executive director of the Syrian Emergency Task Force, an American humanitarian organization that works for democracy in Syria.

Mr. Moustafa said the rebels had taken close note of the damage caused by pager attacks targeting Hezbollah members in Lebanon, and Israeli airstrikes on leaders of Iran’s Islamic Revolutionary Guards Corps in Syria. Those attacks signaled to the rebels that the time was right for one of their own assaults, he said.

He added that a desire to aid Ukraine was another factor prompting the offensive, with the aim of striking a blow against Russia, a mutual enemy, he said.

Mr. Moustafa said he had been aware of preparations to coordinate an offensive in recent weeks. “I knew they had been making plans,” he said in a telephone interview, “but what surprised me was that they took Aleppo in two days.”

The surge in fighting has raised questions for the first time in years about how far the rebels can go and how strong Mr. al-Assad’s grip on power is. And it may disrupt the gradual trend toward acceptance internationally of Mr. al-Assad’s remaining as leader of Syria and the resumption of diplomatic relations with Syria among Arab states and some European nations.

Both Russia and Iran have declared their support for Mr. al-Assad, but beyond several Russian airstrikes on the cities of Idlib and Aleppo, which are both in rebel hands, analysts are questioning how much assistance they will be able to deliver in the immediate term.

Arab states have expressed concern about Syria’s sovereignty being respected, which analysts said was a diplomatic way of criticizing Turkey’s continuing role in backing rebel groups for its own interests.

“Concern in the UAE, Saudi Arabia, Jordan, Iraq & Israel over the potential collapse of the Assad regime & Turkish expansion in Syria,” Hassan I. Hassan, a prominent Syrian journalist and editor of New Lines Magazine, posted on the social media platform X.

Iran’s military activity in Syria has been diminished by Israeli airstrikes that have increased in frequency and potency in the past year. The strikes have knocked out weapons supplies and militia groups as well as killed leaders of Iran’s Islamic Revolutionary Guards Corps who command Iranian militias in Syria and work closely with Syrian military divisions.

The strikes have not only damaged Iran’s freedom to operate in Syria, but have also created suspicion between the allies and their hosts, some Syrian analysts said.

The rebels’ success in securing important military points in and around Aleppo in the past few days, including a military academy on the outskirts of the city, has allowed them to consolidate control, the Omran Center for Strategic Studies, an independent research group based in Istanbul that focuses on Syria, said in a report on Sunday. It also potentially paves the way for new offensive operations, the report said.

“Russia faces a genuine predicament due to the growing challenges of adapting to the evolving battlefield realities, further complicating its ability to provide effective support to the regime,” the center said.

Turkey and the United States both support armed groups in Syria that have fought against groups backed by Russia and Iran.

Turkey supports the Syrian National Army, which is part of the rebel force fighting in Aleppo. It has long been focused on expanding a buffer zone along its border with Syria to guard against the activities of Kurdish militants based in the region that it sees as a threat. It also wants to create an area where it can resettle some of the three million refugees who have fled Syria and are living in Turkey.

The American forces in Syria work with the Kurds, and have armed and equipped a predominantly Kurdish militia, the Syrian Democratic Forces, to fight against the Islamic State, the extremist group that is also active in the region. Both Turkish and American forces have clashed with Russian forces on occasion in Syria.

Despite their dispute over American support for the Kurdish force, Turkey and the United States have managed to avoid direct clashes between their operations in Syria. The Syrian forces allied to each of them negotiated for the Kurdish troops to withdraw from positions without a fight, Mr. Moustafa said.

Mr. Moustafa said there had been and continued to be coordination between the rebels and Ukraine on such issues as countering Russian misinformation and providing medical assistance.

“Two nations are fighting for their country to be free of tyranny and outside occupation,” he said. “It’s natural for them to coordinate.”

Ukrainian officials have not commented on the Syrian offensive, but Kyrylo Budanov, the head of Ukraine’s military intelligence agency, has repeatedly said his forces would seek to attack Russian forces anywhere in the world.

Syrians watching events from outside the country describe this offensive, including the negotiated withdrawals, as distinct from previous periods of fighting. Few believe the government can retake lost territory quickly because of low morale in the army and in government-controlled parts of the country.

In those areas, many people, including government officials, have been reduced to poverty, and that is one of the reasons for the swift collapse of the government forces, analysts say.

Ruhullah Khapalwak and Saad Alnassife contributed reporting.

A deal to end the fighting between Israel and Hezbollah in Lebanon went into effect last Wednesday, but already there have been multiple claims of cease-fire violations by either side.

They have continued to fire on each other, though at a far less intense pace, raising questions about the durability of the truce.

Here’s what to know.

No one is saying the deal has collapsed.

“I’ve been around Lebanon cease-fire agreements for decades, and there was no cease-fire agreement that wasn’t initially broken,” said Aaron David Miller, a senior fellow at the Carnegie Endowment and a former State Department Middle East analyst and negotiator.

The real question, he suggested, is whether the parties have the will to absorb violations and exercise restraint while they get through the initial 60-day phase.

Both sides are making claims of violations.

In statements over the weekend, the Israeli military said it had carried out strikes to enforce cease-fire violations, including killing Hezbollah militants and bombing the group’s facilities.

On Monday, Hezbollah said — and Israel confirmed — that it had fired munitions into a border area known as Shebaa Farms in response to a series of Israeli cease-fire violations, including airstrikes and shootings, over the previous days. It was the first time since the cease-fire that Hezbollah fired into Israel-controlled land. Both Lebanon and Israel claim Shebaa Farms as their own. Hezbollah said the strike was meant as a warning.

Israel’s prime minister, Benjamin Netanyahu, called the Hezbollah strike “a severe violation of the cease-fire” and pledged in a statement on Monday that Israel “will respond forcefully.”

After the strike on Shebaa Farms, the Israeli military said that it had bombarded targets in Lebanon. Israeli strikes on Monday, including those in response to Hezbollah’s actions, killed at least 11 people, said Lebanon’s health ministry, which does not distinguish between civilians and combatants.

What the cease-fire deal really says.

Even amid the strikes, the fragile truce apparently remains in place, and experts say that it could still stick.

Under the terms of the deal, which was brokered by the United States and France, Israel has 60 days to withdraw its military from Lebanon, while Hezbollah is supposed to withdraw north of the Litani River, leaving a buffer in southern Lebanon between the militant group and Israel’s northern border. The Lebanese Army, which is not a party to the conflict, is supposed to oversee and enforce security there.

The Israeli withdrawal is expected to happen in phases. The details are not yet worked out and are supposed to be negotiated with the Lebanese Army and overseen by an international committee chaired by the United States. Israeli officials have said repeatedly that during that time they will respond to any provocation, and they have told civilians not to return yet to southern Lebanon.

The implementation period was written into the deal for a reason, Mr. Miller said. “Hiccups, glitches and violations” are to be expected in the early days — and no one can say yet what that will mean for the ultimate viability of the deal, he said.

“If you can get through 60 days without a collapse of the agreement, then you will have a strategic pause,” he said, which might prove to be viable long-term.

Can the deal hold, even with violations?

The initial claims of infractions show the fragility of the deal and the difficulty of enforcing agreements under international law more broadly, said Jennifer Kavanagh, a senior fellow and director of military analysis at Defense Priorities, a foreign policy institute in Washington. It’s one thing to sign an agreement, she said, and altogether another to enforce it.

Under the terms of the agreement, both Israel and Lebanon can exercise their right to self defense, as long as it’s consistent with international law. The details and enforcement mechanisms remain hazy.

The United States and France, alongside the United Nations, are supposed to play a role in assessing violations. But it is not clear whether any mechanisms are fully in place at this point or how they are supposed to work.

Israel’s leaders have said they will “enforce” the deal militarily, arguing that even small violations could embolden the Lebanese armed group.

Despite the uncertainties, the fact that Israel and Lebanon reached an agreement, and that Hezbollah, which is backed by Iran, said it would abide by the terms, shows that — for now — all involved see benefit to a pause, experts said.

Ms. Kavanagh said she expected violations and failures but was not entirely pessimistic, because all sides “have incentives to make it work.”

The conflict may not be resolved in the long run, Mr. Miller said, but he advised against being overly swayed by daily headlines about violations.

For now, he said, “commitments will be measured over a two-month period.”

Aaron Boxerman and Euan Ward contributed reporting.

When American presidents visit another country, they typically like to highlight the positive history they share. But as the first leader of the United States to visit Angola, President Biden opted instead to focus on the most bitter chapter that connects the United States and this giant southern African nation.

At the National Museum of Slavery in the capital, Luanda, Mr. Biden recalled in a speech on Tuesday the slave trade that once defined relations between America and Angola. More Africans sold into slavery in the United States came from this part of the continent than from anywhere else, scholars say, a legacy of inhumanity that remains relevant four centuries later.

The president’s decision to emphasize that connection served not only as a nod to the injustices inflicted on generations of Africans, but also as a statement of principle in the contemporary debate underway in his own country about how to teach and remember history. At a time when some Republicans have sought to limit instruction about slavery and other shameful chapters of American history, Mr. Biden argued for confronting the past.

“I have learned that while history can be hidden, it cannot and should not be erased,” the president told an audience at the museum, where he was joined by several Black Americans whose descendants were enslaved in Angola and trafficked across the Atlantic Ocean. “It should be faced. It’s our duty to face our history — the good, the bad and the ugly, the whole truth. That’s what great nations do.”

Speaking under a rainy sky on a stretch of the Atlantic Ocean coast where enslaved people were forced onto ships, Mr. Biden called slavery “cruel, brutal, dehumanizing, our nation’s original sin, original sin, one that haunted America and cast a long shadow ever since.” And while the United States has never fully “lived up to that idea” of a truly equal society, he said, “we’ve never fully walked away from it, either.”

Among those on hand for Mr. Biden’s visit was Wanda Tucker, a descendant of William Tucker, believed to be the first enslaved child born in the United States. His parents were brought from Angola to colonial Virginia in 1619 aboard the White Lion, a Portuguese ship. The William Tucker 1624 Society was organized to research and share the stories of the first enslaved people brought to Virginia.

“It’s incredibly awesome to have the president of the United States to come to the homeland where the first enslaved people were taken from,” Ms. Tucker said in an interview outside the museum, which was founded in 1977 and will receive a U.S. grant of $229,000 to support restoration and conservation.

“It’s even more important because we have to keep the history and the story going wherever there are opportunities to tell the story,” Ms. Tucker said.

While many Americans focus on countries like Senegal and Ghana when tracing the history of slavery, Angola was a major center for the capture and sale of human beings. As many as 6 million people were kidnapped from this part of Africa, forced to march as much as 100 miles and loaded onto ships to the Western Hemisphere. Slavery “would decimate the Angolan population for over 300 years,” Daniel Metcalfe wrote in “Blue Dahlia, Black Gold,” his 2013 book on modern Angola.

About a quarter of all enslaved Africans forced to go to the United States came from the area that includes modern-day Angola, according to SlaveVoyages, a digital database. Today, there are nearly 12 million Americans of Angolan descent, according to the U.S. government.

Long before coming to Angola for the first and only trip to sub-Saharan Africa of his presidency, Mr. Biden had taken steps to reckon with the history of racism and slavery in America.

Shortly after he came into office, he made Juneteenth a federal holiday to commemorate the end of slavery in the United States. His vice president, Kamala Harris, in 2023 visited the Cape Coast Castle in Ghana, a site used for the slave trade in the 17th century.

Mr. Biden also has at times expressed concern over the attempts in the United States to restrict how the less-flattering parts of American history are taught. He screened the movie “Till,” about the 1955 murder of Emmett Till, a Black 14-year-old, in the same White House theater where, in 1915, President Woodrow Wilson premiered “The Birth of a Nation,” a film celebrating the Ku Klux Klan.

Mr. Biden later established a national monument honoring the slain teenager and his mother, Mamie Till-Mobley, just as Gov. Ron DeSantis of Florida came under fire after education officials in his state decreed that middle schoolers should be taught that enslaved people benefited by developing skills from slavery.

In May, Mr. Biden spoke to a crowd at the National Museum of African American History and Culture to celebrate the 70th anniversary of Brown v. Board of Education, the landmark civil rights ruling that outlawed racially segregated schools. As a senator, Mr. Biden cosponsored legislation to establish the museum.

But in his speech on Tuesday, Mr. Biden also pivoted forward to stress how far the United States and Africa had come since those days of misery. He pointed to U.S. investments and other commitments to the continent, where Angola is an important source of oil and minerals.

Mr. Biden met with President João Lourenço, who has made a point of bolstering relations with the United States and visited the White House during Mr. Biden’s term. Like other presidents, Mr. Biden said he had worked to transform the relationship with Africa from one based on aid to one based on trade.

“The United States is expanding our relationship all across Africa from assistance to aid, investment to trade, moving from patrons to partners to help bridge the infrastructure gap,” he said. “The right question in the year 2024 is not what can the United States do for the people of Africa. It’s what can we do together for the people of Africa.”

Mr. Lourenço welcomed his guest, saying that Mr. Biden’s decision to visit Angola marked a “turning point” for the two nations. He applauded Mr. Biden’s “great contribution” to the development of Angola through the Lobito Corridor project, a U.S.-funded rail line that will link Angola with Zambia and the Democratic Republic of Congo.

Left unmentioned both in public and in the private meeting with Mr. Lourenço, according to American officials, was the incoming president, Donald J. Trump, whose imminent takeover of the White House has loomed over Mr. Biden’s visit. Mr. Trump never visited Africa while president, and referred to some of its countries using an epithet.

Mr. Biden brought with him a delegation of American political, civic and business leaders.

“It’s important that we’re here because of the historical significance, but the president also made a commitment to look at Africa, to invest in Africa,” Derrick Johnson, the president of the N.A.A.C.P., said in an interview. “We need to work with the African nations to rebuild and strengthen the infrastructure.”

Hospitals have been ripped apart by airstrikes. Nearly 50,000 people have fled their homes, and tens of thousands lack running water. Civilians are being laid out in body bags on hospital floors after shells struck their neighborhoods.

Scenes from the bloodiest days of Syria’s civil war, which had lain largely dormant for several years, are now repeating themselves in the country’s northwest as pro-government forces try to beat back a surprise rebel offensive, according to aid workers, a war monitor and the United Nations, who warned of a rapidly worsening humanitarian situation.

Conditions were already dire for civilians in the area: Years of war and a powerful February 2023 earthquake had led to crushing poverty, displacement and breakdowns in services. But over the last several days, the region’s misery deepened as Russian and Syrian fighter jets have repeatedly struck Idlib and Aleppo in northwestern Syria and rebels fought to capture more territory.

The United Nations said more than 50 airstrikes had hit Idlib Province in northwestern Syria on Sunday and Monday. Four health facilities, four schools and two camps housing people displaced from earlier phases of the conflict suffered damage, it said.

Stéphane Dujarric, a U.N. spokesman, said in a briefing Monday night that a strike on a water station had also cut off access for at least 40,000 people. And the Norwegian Refugee Council, which provides aid in the region, said its humanitarian workers were reporting that bakeries and shops had shut down in Aleppo, leading to food shortages.

NATO’s new top diplomat suggested on Tuesday that Ukraine should put off any peace talks with Russia until Western allies can send enough military aid to help Kyiv push ahead on the battlefield and garner a stronger negotiating position.

Mark Rutte, the NATO secretary general, said it was up to Ukraine to decide when it was ready to begin negotiations with Russia in a war that has dragged on for nearly three years.

But with U.S. President-elect Donald J. Trump vowing to secure a quick cease-fire that officials in Kyiv fear would be favorable to Russia — and despite war fatigue hanging over parts of Europe — Mr. Rutte urged the military alliance’s members to step up shipments of weapons, ammunition and air defenses before they try working toward a truce.

“Let’s not have all these discussions, step by step, on what a peace process might look like,” Mr. Rutte said ahead of two days of meetings of foreign ministers, including Ukraine’s, at NATO headquarters in Brussels. “Make sure that Ukraine has what it needs to get to a position of strength when those peace talks start.”

“So I would say more military aid, and less discussions on what the peace process could look like,” Mr. Rutte added.

His comments came even as President Volodymyr Zelensky of Ukraine has recently shifted his public stance on a potential peace deal. After years of insisting that Ukraine would cede no territory to Russia in a deal, he has recently signaled that Ukraine would be willing to do so — for now, at least — in return for NATO membership.

While NATO membership remains unlikely while the war is ongoing, Mr. Zelensky’s rhetoric is a marked change. Officials in Kyiv have even provided a rationale that could potentially allow them to temporarily cede territory, asserting that Russian-controlled land in Ukraine would not be internationally recognized as part of Russia.

On Sunday, Mr. Zelensky also admitted that Ukraine’s army couldn’t liberate some of the estimated 20 percent of its territory that Russia occupies, including Crimea. “Our army lacks the strength to do that,” Mr. Zelensky told the Japanese news agency, Kyodo News.

Mr. Zelensky has remained adamant, though, that Ukraine must become a full member of NATO immediately to guarantee its security, even if Russian-occupied areas do not receive full alliance protection.

In a statement Tuesday, Ukraine’s foreign ministry pointedly cited a 1994 treaty that guaranteed the country’s peace and territorial sovereignty in exchange for giving up its nuclear arsenal. Russia violated that agreement, known as the Budapest Memorandum, with its incursion into Ukraine in 2014, which led to the full-scale invasion in 2022, the statement said.

“With the bitter experience of the Budapest Memorandum behind us, we will not accept any alternatives, surrogates or substitutes for Ukraine’s full membership in NATO,” it said.

The alliance has declared Ukraine’s eventual membership as “irreversible,” but NATO states are divided on how soon it should be allowed in.

Recently there have been a swirl of proposals to end the fighting as Ukraine struggles to maintain its foothold on the front lines. Although Russian soldiers are being killed and wounded at an unprecedented rate in this war — averaging as many as 1,500 a day in November, according to intelligence estimates — Ukraine is steadily losing miles of territory where, just months ago, the two sides fought over mere yards.

Mr. Trump has been vague about how he would bring peace to Ukraine in as little as 24 hours, as he has pledged. But senior officials in his administration, including Vice President-elect JD Vance, have proposed such ideas as allowing Russia to keep the territory it has captured and guaranteeing that Ukraine will not join NATO, or withholding military aid to Ukraine until it agrees to negotiate.

More than half of the military aid that Ukraine receives comes from the United States, which has sent more than $61 billion in weapons and equipment since the full-scale war began in February 2022.

But senior NATO officials said Tuesday that President Vladimir V. Putin of Russia appears uninterested in negotiating peace while he is gaining ground — unless the deal being discussed is to his advantage.

“It’s not in our interest, none of us, if Putin wins this war,” Admiral Rob Bauer of the Netherlands, NATO’s top military officer, said in a brief interview. “Wars can change — and the situation can change, based on what we do.”

Far from approaching peace, the war has escalated in recent weeks.

Last month, Ukraine launched long-range American and British artillery into Russia for the first time, prompting Moscow to accuse NATO of becoming a direct participant in the war. Russia countered within days by firing an experimental ballistic missile designed to carry nuclear weapons at a weapons factory in eastern Ukraine. The missile caused limited damage, but Mr. Rutte said on Tuesday that its use sought to intimidate “those who support Ukraine as it is defending itself.”

In recent days, Estonia, Germany, Lithuania, Norway, Sweden and the United States have provided hundreds of millions of dollars in ammunition, air defenses and other arms as the allies try to demonstrate they are stepping up support to Ukraine and the Biden administration pushes as much American matériel to the war before Mr. Trump takes office in January.

“We need this certainty,” said Ukraine’s foreign minister, Andrii Sybiha. “We need strong decisions to strengthen us, to strengthen our capacities.”

Mr. Sybiha said Ukraine needed at least 19 more air defense systems to protect its people and energy infrastructure from Russian attacks.

The effort is particularly dire as bitter cold sets in, in Ukraine, “with once again Putin, weaponizing winter, trying to freeze people out of their homes, turn out the lights,” Secretary of State Antony J. Blinken said. “We’re not going to let that happen.”

John Leung was an unlikely spy. In the small Oklahoma town where he lived, people knew him as a former restaurant owner and a father. In Houston, where he often traveled, they knew him as a political organizer in the city’s vibrant Chinese community.

And in China, they knew him as a benevolent patriot, a man who arranged musical performances and embraced official causes like unifying the mainland with Taiwan.

In fact, Mr. Leung was an informant for the F.B.I., gathering intelligence on China, according to two senior United States officials. That work landed him in Chinese custody in 2021, after he traveled to the mainland at the age of 75. He was later sentenced to life in prison, a first in decades for an American accused of espionage.

Mr. Leung was freed last Wednesday in a rare prisoner swap between Washington and Beijing. Six months shy of his 80th birthday, he was put on a plane to the United States with two other Americans who had been detained in China, along with three Uyghurs, members of an ethnic group that faces repression by the Chinese government.

In return, Washington released Xu Yanjun, a convicted Chinese spy who had been serving a 20-year sentence, and Ji Chaoqun, 31, who had reported to Mr. Xu and was serving an eight-year sentence. A clemency order for a third Chinese national, Jin Shanlin, who had been in prison for possessing child pornography, was signed on the same day as an order for Mr. Xu. China said Washington also handed over a fugitive.

Mr. Leung had cultivated an image as a philanthropist, which brought him access to Chinese power circles. In Houston, he directed groups that promoted Beijing’s political interests. He attended Chinese state banquets. And he rubbed shoulders with senior Chinese officials, including its foreign minister, its ambassador and three consuls general to the United States.

But that carefully curated image was a ruse.

To piece together the story of Mr. Leung’s unusual trajectory from small-town restaurateur to prisoner in a high-stakes geopolitical dispute with China, The Times interviewed dozens of people who knew him, including relatives in the United States and Hong Kong, business associates in Houston and acquaintances in New York’s Chinatown. Reporters also drew on corporate records, archival materials and other documents.

Much remains unclear about Mr. Leung’s relationship with the F.B.I. China’s Ministry of State Security said that he was spying while in China, but U.S. officials said that Mr. Leung had not worked for the F.B.I. for years and that the bureau had discouraged him from making the trip.

Some of the pro-China groups Mr. Leung was involved with have been linked to organizations that have come under U.S. government scrutiny. One was affiliated with the National Association for China’s Peaceful Unification, which the Trump administration designated in 2020 as a foreign mission, accusing it of seeking “to spread Beijing’s malign influence in the United States.”

“Chinese intelligence operatives are known to use these organizations as cover for their clandestine operations,” said Dennis Wilder, a former U.S. intelligence analyst on China and a senior fellow at Georgetown University.

Mr. Leung’s work with such groups could have made him a useful informant, said Nigel Inkster, the former director of operations and intelligence for Britain’s Secret Intelligence Service. He described Mr. Leung as a likely “access agent,” with “no access to secrets himself but access to people who might have them.”

Christopher Wray, the F.B.I. director, has called Beijing the “biggest long-term threat to our economic and national security.”

China’s spy agency has publicized what it portrays as Mr. Leung’s treachery, saying that he “collected a significant amount of intelligence related to China.” The ministry said he lured Chinese officials into U.S. hotel rooms for “pornographic traps,” an allegation that former and current bureau officials said was false, explaining that the F.B.I. does not use such tactics.

The Chinese spy agency also released a video of Mr. Leung made while he was in custody, in which he expressed regret for what he had done. (Prisoners in China have in the past been coerced into making such televised confessions for propaganda purposes.)

Mr. Leung, who upon arriving in the United States was sent to an Army medical center outside San Antonio, could not be reached for comment. He was met there by a son, according to Nury Turkel, a lawyer who was there to welcome his mother, one of the Uyghurs released by Beijing. Calls and messages left for family members were not returned.

David Tang, a director with Mr. Leung of several pro-China groups in the Houston area, said he was happy to hear the news that Mr. Leung was back in the United States. He said he did not believe that he was a spy and that his release pointed to his innocence. “The mistake finally was corrected.”

An Arrest, and Charges Dropped

Mr. Leung was born in 1945 in Hong Kong’s New Territories, a largely mountainous, lush expanse of villages and farmland. He moved to New York in the 1970s, where he worked a low-level mailroom job at the United Nations while starting travel agencies in Chinatown with his brothers.

The travel business boomed. One agency, Leung Brothers Travel, had offices in New York and Toronto. It was the exclusive booking agent for Singapore Airlines, which often made it a necessary stop for people hoping to travel to Asia, said Tom Yiu, a longtime travel agent in Toronto.

New York’s Chinatown was roiled by crime, with Chinese gangs waging bloody turf wars, and Mr. Leung ran a side business selling guns, according to two longtime acquaintances. In 1980, his partner at a second travel agency was shot dead by two masked men while Mr. Leung crouched in the bathroom, according to acquaintances and to Chinese-language news reports from the time.

A few years later, he moved with his wife at the time, Kin Lan Ng, to Durant, a small college town in southeastern Oklahoma. The couple opened a Chinese restaurant in a strip mall, bought a modest home and raised three sons, according to property and ancestry records, and an interview with one son, Kit Leung.

In 1984, Mr. Leung was arrested in Durant in the attempted purchase of a .22-caliber pistol and a silencer from an undercover federal agent. He was charged with possession of an unregistered firearm, court records show.

Rick Musticchi, a former agent with the Bureau of Alcohol, Tobacco, Firearms and Explosives who sold Mr. Leung the gun and silencer, told The Times that he had approached Mr. Leung after getting a tip from an informant that he was involved in illegal activity and preparing to travel to China.

Mark F. Green, Mr. Leung’s lawyer on the case, said that prosecutors dropped charges after Mr. Musticchi did not show up to a hearing.

China’s spy agency said that U.S. intelligence operatives first contacted Mr. Leung soon after, in 1986, and formalized the relationship in 1989. The Times could not verify those allegations.

For a small-town restaurant owner, Mr. Leung soon developed unusually high-level connections inside China, which was opening to the West. He set up a group that promoted business and cultural ties between Oklahoma City and the southern Chinese city of Guangzhou, according to corporate records.

Mr. Leung also organized musical exchanges between Southeastern Oklahoma State University, The Juilliard School in New York and cities in China. He arranged for the Chinese classical pianist Li Yundi to perform in Oklahoma in 1999.

The performances he set up in China were sometimes disorganized, said Aaron Wunsch, a Juilliard pianist who joined several of them. Mr. Wunsch said he once arrived to find the piano wrapped in plastic and missing legs. But, he added: “He would talk in a genuine way about China and how he loved China and the U.S.”

Mr. Leung’s efforts earned him accolades inside China. In 2004, he was featured as one of 55 “outstanding overseas Chinese representatives” in People’s Daily, the Communist Party’s mouthpiece.

At a 2008 state banquet in Beijing celebrating the founding of China, he posed for a photo with Yang Jiechi, then the foreign minister, said Mr. Tang, who had also attended the event.

Li Liangzhou, a now-retired director of Guangzhou’s foreign affairs office, helped Mr. Leung organize many of the exchange trips. “He didn’t ask us about inside government information,” Mr. Li said in a phone interview in March. “We didn’t expect him to be a spy at all.”

Expanding Into Houston

In the mid-2000s, Mr. Leung began setting up pro-China groups in Houston, which was home to a large Chinese community and a Chinese consulate.

There, Mr. Leung drafted an alternative past. Mr. Tang, the other organizer of the pro-China groups, said he met Mr. Leung at a party in Houston, and they bonded by speaking Cantonese. Mr. Leung, who sometimes donated money to their groups, said he had come from wealth. He said he owned ranches in Oklahoma, sometimes showing up with farm eggs. He did not mention having owned a restaurant, despite the fact that his new friend was also a restaurateur, according to Mr. Tang.

The two joined forces in the Texas Council for the Promotion of China’s Peaceful Reunification, a group with links to the Washington, D.C.-based group the Trump administration later designated as a foreign mission.

Mr. Tang rejected the Trump administration’s characterization and said the group was set up to support American policy on China. He said he and Mr. Leung attended a 2018 protest against a stopover in Houston by Tsai Ing-wen, Taiwan’s president at the time.

Mr. Leung also became a director of the Chinese Civic Center in Houston, according to its tax filings. It serves the Chinese community and houses a separate service center that has come under scrutiny for suspected ties to Beijing. In 2023, the Justice Department accused two men of operating an “illegal overseas police station” out of a similar outpost in New York.

Xie Bin, a cybersecurity specialist in Houston, said he met Mr. Leung during this period at a mid-autumn festival event attended by Chinese diplomats. “He was the one who greeted everyone,” Mr. Xie said.

But Mr. Leung never found a home in Houston, said Mr. Tang, staying instead at a Ramada close to Chinatown.

The Chinese government’s efforts in Houston were becoming a focus for the F.B.I. Beginning in 2018, the bureau spent over a year investigating suspected intellectual property theft at Texas Medical Center by researchers with ties to China.

Relations deteriorated, and the Trump administration closed the Chinese consulate in Houston in July 2020, saying it was a hub of spying. Beijing responded by shuttering the U.S. consulate in Chengdu.

From a Life Sentence to a Surprise Release

In 2023, a Chinese court said Mr. Leung had been arrested two years earlier by state security agents from Suzhou, a city in Jiangsu Province. He had traveled to Jiangsu regularly for years, making inroads there with officials.

In China, where the top leader, Xi Jinping, has empowered security agencies to hunt down spies, Mr. Leung’s arrest and life sentence were hailed as a win.

In the United States, Mr. Leung’s case got little news coverage.

Kit Leung said in January at his home in Texas that Mr. Leung took him and a brother to Hong Kong to witness its handover to Chinese control in 1997 but that he and his father later became estranged. He said he learned about his imprisonment through news reports. Mr. Leung’s ex-wife, Ms. Ng, a New York resident, said she hadn’t spoken to him in years.

Another son moved into Mr. Leung’s house in Durant, neighbors said, and told them that his father had died. Reached there in January, that son, Carl Leung, declined to comment.

But under intense secrecy, the Biden administration was working out the contours of a swap with Beijing. During a global summit in Peru last month, President Biden discussed a potential trade with Mr. Xi.

When Mr. Leung and the two other American prisoners were released, they were met by Nicholas Burns, the U.S. ambassador to China, at the Beijing airport. He handed them their U.S. passports. President Biden and Secretary of State Antony J. Blinken separately called all three men when they landed in Alaska for refueling.

For Mr. Leung, it was the end of his time in Chinese custody — as well as the end of a ruse.

Edward Wong, Isabelle Qian, Chris Buckley, Keith Bradsher and Mattathias Schwartz contributed reporting. Jack Begg and Kirsten Noyes contributed research.

Giulia Cecchettin was just days away from graduating with a degree in biomedical engineering at the University of Padua, in Italy, when her disgruntled ex-boyfriend confronted her, demanding that she take him back. Her body was found a week later, wrapped in plastic bags and thrown in a ditch. She had been stabbed more than 70 times.

On Tuesday, more than a year after Ms. Cecchettin’s killing, her former boyfriend, Filippo Turetta, was convicted of murder and sentenced to life in prison, concluding a case that has outraged people across Italy, where chauvinistic attitudes remain deeply rooted at all levels of society.

In the first 11 months of this year, 101 women were killed in Italy, more than half by their current or former partners, according to Italy’s Interior Ministry. But Ms. Cecchettin’s story has stood out, striking a particularly deep chord across the country.

She was just 22 years old. Her life was about to take off. That it was cut short so brutally highlighted for many people the country’s failures to address the root problems of the pervasive violence.

Mr. Turetta, 22, confessed to the killing soon after he was arrested a year ago. When he took the stand in a court in Venice last October, he said he had been “upset” because Ms. Cecchettin broke up with him and refused to take him back.

“I was suffering a lot and I resented her,” he said. “I was angry because this made me suffer, and it upset me.”

Some three weeks after Ms. Cecchettin’s body was found, thousands congregated for her funeral. When the coffin was borne out of the church, the mourners jingled their keys, heeding the call of her older sister, Elena Cecchettin, who had called on Italians to protest violence against women and “make noise” rather than hold a minute of silence to commemorate Giulia’s death.

Since Ms. Cecchettin’s death, her father, Gino Cecchettin, and Elena Cecchettin have campaigned ceaselessly against gender violence.

In order to help promote “a radical change” in the mind-set of Italians, the family set up a foundation last month in Ms. Cecchettin’s name. Its goal is to promote better education in schools about domestic violence and to help women who have been victims of violence.

But the inauguration of the foundation was marked by controversy after Italy’s education minister, Giuseppe Valditara, sent a video in which he said that patriarchy no longer existed in Italy. He also blamed illegal immigration for violence against women. The video was met with nationwide backlash.

A few days later, Prime Minister Giorgia Meloni dug in her heels and defended Mr. Valditara.

“There is certainly data that also speaks of a significant incidence of mass illegal immigration on this issue,” she said, and this “is one of the reasons Italy is working to stop mass illegal immigration.” She said that cultural reasons were also at play and that the government was committed to combating “a scourge.”

Elena Cecchettin responded on social media, saying that instead of spreading propaganda “at the presentation of the foundation named after a girl killed by a white, Italian, ‘decent boy,’” the authorities should instead listen to the Italian people. That way, “hundreds of women in our country would not continue to die every year,” she said.

After Tuesday’s ruling, Mr. Cecchettin told reporters, “I think you don’t fight against gender violence with jail sentences, but with prevention.”

“My feeling is that we have lost, all of us, as a society,” he said, the news agency ANSA reported. Justice has been done, and should be respected, he said, but “as a human being I feel defeated.”