In the turbulent landscape of the Middle East, Iran’s aging supreme leader, Ayatollah Ali Khamenei, could always rely on the close alliance, unwavering loyalty and deep friendship of Hassan Nasrallah, the leader of the Lebanese militia Hezbollah.

When Israel killed Mr. Nasrallah in a massive airstrike on Friday, it abruptly wiped out a singular force in Ayatollah Khamenei’s hierarchy of close associates.

Iran had for 40 years nurtured Hezbollah as the main arm of its proxy network of militias, as a forward defense against Israel. But in the past two weeks, Hezbollah’s capacity began to crumble under wave after wave of Israeli attacks on its leadership, arsenal and communications.

Now, fissures have opened within the Iranian government over how to respond to Mr. Nasrallah’s killing, with conservatives arguing for a forceful response and the moderates, led by Iran’s new president, Masoud Pezeshkian, calling for restraint.

All of this has left Iran, and its supreme leader, in a vulnerable position.

Four Iranian officials who knew Mr. Nasrallah personally and had been briefed on events said that Ayatollah Khamenei had been deeply shaken by his friend’s death and was in mourning but had assumed a calm and pragmatic posture. The officials, including two members of the Islamic Revolutionary Guards Corps, requested anonymity, as they were not authorized to speak publicly.

Ayatollah Khamenei struck much the same tone in public. Instead of lashing out at Israel, he issued two restrained statements, praising Mr. Nasrallah as a leading figure in the Muslim world and the network known regionally as the axis of resistance, and saying that Iran would stand by Hezbollah.

Significantly, Ayatollah Khamenei signaled that it would be Hezbollah, not Iran, that would be leading any response to Israel, and that Iran would play a supporting role. “All of the forces in the resistance stand by Hezbollah,” he said. “It will be Hezbollah, at the helm of the resistance forces, that will determine the fate of the region.”

It was a striking sign, some analysts said, that Ayatollah Khamenei may have no way to respond effectively at the moment to Israel’s onslaught on his proxies. Faced with a choice between all-out war with Israel or lying low in the interest of self-preservation, he appears to be choosing the latter.

“They are completely checkmated by Israel at this moment,” said Sanam Vakil, the director for the Middle East at Chatham House. “Khamenei’s statement is indicative of the gravity of the moment and the caution; he is not publicly committing to anything that he can’t deliver.”

After Ayatollah Khamenei’s statements, a flurry of reactions from senior Iranian officials and military commanders had the same cautious tone, outsourcing revenge to other militia groups in the region. Gen. Hossein Salami, the commander in chief of the Revolutionary Guards, said it would be “Hezbollah, Hamas and other Palestinian militants” that would deliver blows to Israel.

In Tehran, the news of Mr. Nasrallah’s death cast a pall of shock and anxiety over senior officials who wondered in private phone calls and during emergency meetings if Israel would strike Iran next, and if Ayatollah Khamenei would be its next target, the four Iranian officials said in telephone interviews.

“This was an incredibly heavy blow, and realistically speaking, we have no clear path for recovering from this loss,” Mohammad Ali Abtahi, a former vice president of Iran, said in an interview from Tehran on Saturday. “We will not go to war, that’s off the table. But Iran will also not reverse course in supporting the militant groups in the region, nor in defusing tensions with the West. All of these things can be pursued at the same time.”

Mr. Abtahi said the collective feeling among Iranian officials was one of “shock, anger, sadness and a lot of anxiety.”

This was far different from the sentiment after Hamas’s Oct. 7 attacks on Israel, when Iran and its other proxies celebrated the surprise incursion. At that time, Hezbollah almost immediately attacked Israel’s north with rockets and continued exchanging fire. Iran gradually activated its network of militant groups known collectively as the “axis of resistance” to open fronts against Israel and create chaos in the region to pressure both the United States and Israel into a cease-fire with Hamas.

For Iran, the gamble was to keep the pressure percolating without setting off an all-out regional war.

In many ways, the yearlong confrontation between Iran and its proxies and Israel came to a violent head when Mr. Nasrallah was killed. Iran’s effort to weaken Israel through its proxies has appeared to backfire, leading to a catastrophic blow against its most strategic ally.

When the news broke that Israel had most likely killed Mr. Nasrallah, Ayatollah Khamenei convened an emergency meeting of the Supreme National Security Council at his home, the Iranian officials said. During the meeting, people were divided on how to respond.

Conservative members, including Saeed Jalili, an influential former presidential candidate, argued that Iran needed to establish deterrence quickly with a strike on Israel, before Israel’s prime minister, Benjamin Netanyahu, brought the war to Tehran, according to officials familiar with the meeting.

Iran’s new president, Mr. Pezeshkian, who spent last week telling world leaders at the United Nations General Assembly that his government wanted to defuse tensions and get along with the West, argued against such a response, saying that Iran should not fall into a trap being set by Mr. Netanyahu for a wider war, the Iranian officials said.

Other moderate voices on the council argued that Mr. Netanyahu had blown through all red lines, and that if it assaulted Israel, Iran could face dire attacks on its own critical infrastructure, something the country could not afford, those officials said, particularly given the dire state of the economy.

But state television, run by Mr. Jalili’s affiliates, called for Iran to strike Israel, in open defiance of Ayatollah Khamenei’s caution. “There is no difference between Tehran and Baghdad and Beirut; the regime will come after each of these targets,” the anchor of state television said. “Netanyahu only understands one language, and that’s ballistic missiles and drones.”

Domestically, Iran has faced a cascade of challenges, from public discontent against government corruption and mismanagement of the economy and widespread hardship to Israel’s infiltration into Iran’s military and political ranks.

In New York, Mr. Pezeshkian told reporters that Iran was ready to “lay down its arms if Israel laid down its arms,” and called for an international force to intervene in establishing peace in the Middle East.

Mr. Pezeshkian has had to contend with two major crises during his two months in office: the Israeli assassination of the Hamas political leader, Ismail Haniyeh, in Tehran on the night of his inauguration and Mr. Nasrallah’s killing on the eve of his birthday.

Those crises made him an easy target among conservatives in Iran who criticized his conciliatory message in New York, saying it showed weakness and emboldened Israel to kill Mr. Nasrallah. The conservatives argued Iran should deploy fighters to Lebanon, as it did for the Syrian government in its civil war, to help Hezbollah in the event of an all-out war with Israel.

“Israel has attacked the nucleus cell of the resistance and thus we cannot be indifferent,” said a conservative cleric, Ayatollah Mohammad Hassan Akhtari, the head of Iran’s Committee to Support Palestinians and the former head of international relations in Ayatollah Khamenei’s office.

Two members of the Revolutionary Guards — including a strategist who had been in planning meetings for the past two days on how Iran should respond — said in interviews that Iran’s immediate priority was to help Hezbollah get back on its feet, name a successor to Mr. Nasrallah, line up a new command structure and rebuild a safe communications network. Then, Hezbollah can plan its retaliation against Israel, they said.

Iran was planning to send a senior Quds Forces commander to Beirut by way of Syria to help guide Hezbollah’s recovery, the two Revolutionary Guards members said.

Ayatollah Khamenei announced five days of mourning in Iran, but across the country, the reaction to Mr. Nasrallah’s death was mixed. Supporters of the government staged public mourning ceremonies in Tehran’s Palestine Square. They waved the yellow flag of Hezbollah and chanted, “revenge, revenge,” and “death to Israel.”

But among dissidents, victims of the government’s brutal crackdowns and many ordinary Iranians, Mr. Nasrallah was viewed as an arm of the regime’s oppression. They rejoiced at his death, dancing in the streets and passing boxes of sweets at traffic stops in several cities, according to witnesses. Cars that passed by honked their horns in support.

Quebec is working hard to fortify its official language — much to the displeasure of some who don’t speak it.

Battling what many describe as the incursion of English has become a resounding political message in the province, North America’s largest French enclave. And Quebec’s government is finding more ways to lift the supremacy of French, the province’s lingua franca.

Provincial laws mandate that English text on storefront signs be half the size of French words and that employers reveal what percentage of their staff cannot work in French. New immigrants are given a six-month grace period before French becomes the only language in which they receive government services, such as taking a driver’s test.

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He calls himself the “Volkskanzler,” or people’s chancellor, a term associated with the Nazis.

He has demanded stopping all new asylum seekers to make Austria a “fortress of freedom.” He calls his political opponents “traitors” and has said he wants to put unfriendly journalists on “arrest lists.” The World Health Organization, he has warned, is a dictatorship.

To the growing ranks of his supporters, Herbert Kickl, the chancellor candidate of the far-right Austrian Freedom Party, coolly diagnoses the country’s problems and offers reasonable solutions. To his detractors, the former interior minister is a dangerous right-wing extremist who trades in conspiracy theories.

But after Austrians vote in a national election on Sunday, Mr. Kickl may end up as the man Austria’s other parties will have to either work with or work around.

Five years after his party was ousted by a jaw-dropping scandal involving cocaine, a fake niece of a Russian oligarch, influence peddling and a secret video recording, the Freedom Party is back, and is now the most popular party in Austria.

It could come out on top for the first time ever in elections. The party is expected to win 27 percent of votes or more, polls show, beating out the incumbent center-right Austrian People’s Party by several percentage points, and other mainstream parties by even more.

Unlike in neighboring Germany, where the growing popularity of the far-right Alternative for Germany, or AfD, has set off anxious hand-wringing in the political establishment, in Austria few seem especially concerned by the rise of the Freedom Party.

Founded by former SS men in the 1950s, the Freedom Party has long been part of Austria’s political landscape. It has been the junior partner in four separate governments since the 1980s.

The party “is so normalized in Austria that few people will be shocked by it — and they have already had parliamentary election results on this scale,” said Laurenz Ennser-Jedenastik, a professor of Austrian politics at the University of Vienna.

In Germany, mainstream parties have vowed never to work with the AfD. And the German domestic intelligence service has labeled some AfD state chapters as extremist and is actively monitoring the party, which it considers a threat to the Constitution.

Austria is more akin to Italy or the Netherlands, where anti-immigrant sentiment has fueled the rise of far-right parties that work within the established political ecosystem.

Mr. Kickl often praises Hungary, where the nationalist Fidesz party has governed virtually unopposed for more than a decade, for its ability to keep out migrants.

The coronavirus pandemic and Austria’s strict lockdown rules helped Mr. Kickl re-energize his party after it was kicked out of the government five years ago. Mr. Kickl demanded a public inquest into government actions around lockdowns, which he called “dictatorial.” At the time of the pandemic, Mr. Kickl was a proponent of the anti-parasite drug ivermectin.

At the height of the pandemic in 2021, he told supporters: “The Austrian population is part of a large field study by pharmaceutical companies.”

But much of his focus in the recent campaign has been on immigrants. Besides calling for more deportations, the Freedom Party’s platform also demands new legislation that would stop refugees from getting any social services and bar them for life from obtaining Austrian citizenship.

Besides refugees, Mr. Kickl attacks supranational institutions, like the European Union, NATO (of which Austria is not a member), the International Criminal Court and the World Health Organization as meddling in Austrian affairs.

The party is also close to Russia. In 2016, it signed a formal declaration of friendship with President Vladimir V. Putin’s party, United Russia. Karin Kneissl, the Freedom Party’s choice for foreign minister in 2017, moved to Russia after its invasion of Ukraine. While the rest of Europe has mostly cut off its use of Russian energy since the invasion, Austria has not done so.

Mr. Kickl, 55, has portrayed himself as a kind of father figure to voters but has kept his private life mostly out of the spotlight. He started working for the Freedom Party as a student in history and philosophy, and he quickly rose through the ranks.

He served as a speechwriter for Jörg Haider, who took over the party in 1986 and moved it further toward far-right populism. Mr. Kickl was responsible for some of his most incendiary speeches. Mr. Haider, who later left the party and created a new one, died in a car accident in 2008.

As Austrian interior minister from 2017 to 2019, Mr. Kickl focused on border security, but he may be best remembered for overseeing a raid on the country’s domestic intelligence agency. At the time, Mr. Kickl’s clear political influence over the service made it a pariah among partner agencies.

In rallies, debates and advertisements, Mr. Kickl has distanced himself from his party’s former coalition partner, the conservative Austrian People’s Party, which was itself roiled by a scandal involving fake polls in recent years.

Mr. Kickl now blames his biggest opponent for inflation and a declining standard of living.

“We have actually come through difficult times reasonably well, as far as the Ukraine war is concerned,” said Nina Horaczek, who has written a book on Mr. Kickl. “But at the same time, there is an incredible dissatisfaction in parts of the population, and he is channeling that very, very well.”

Karl Nehammer, the current chancellor, said that if the Freedom Party won, he would not form a coalition government that would make Mr. Kickl chancellor. But he has stopped short of vowing not to work with the far-right party itself, something that experts say could happen if the People’s Party comes in first, thus ensuring that Mr. Nehammer remains chancellor.

If the far right wins, Mr. Nehammer could choose to isolate the Freedom Party and form a government with center-left Social Democrats and possibly a third party.

But a coalition between the conservatives and the far right is still considered a likely outcome, “simply because the parties are relatively close on many issues,” said Thomas Meyer, a politics professor at the University of Vienna.

Predicting the outcome has been made even harder this year by two tiny parties — the Austrian Communists and the Beer Party — that are close to reaching the 4 percent needed to enter the 183-seat Parliament.

Severe flooding in early September also led to a suspension of national campaigning and may give a boost to the Greens, a junior partner in the current government.

On a recent evening in Simmering, a working-class district in Vienna, Sascha Kaiser, a resident, was having a drink after work and mulling whom to vote for. “I don’t know whether to vote strategic or follow my heart,” he said. “But I don’t want Kickl to get in.”

Benjamin Netanyahu’s decision to assassinate Hassan Nasrallah, the Hezbollah leader, capped an increasingly brazen sequence of escalatory moves that reflected the Israeli prime minister’s renewed confidence in Israel’s military strength as well as in his own ability to navigate and defy foreign criticism, analysts said.

Mr. Netanyahu’s authorization of the strike came a day after the United States, Israel’s main benefactor, called for a cease-fire between Israel and Hezbollah. It occurred on the same afternoon that foreign diplomats walked out of his speech to the United Nations General Assembly, protesting the conduct of Israel’s wars in Gaza and Lebanon. And it came amid growing pressure on judges at the International Criminal Court to order his arrest on war crimes charges.

Last October, Mr. Netanyahu canceled a similar attack against Mr. Nasrallah following American pressure to call it off and internal doubts about Israel’s ability to fight on two fronts in Gaza and Lebanon after its failure to prevent Hamas’s Oct. 7 attack on southern Israel. His popularity plummeted after the Hamas raid, with polls repeatedly suggesting that he would easily lose power if a snap election was called.

Nearly a year later, Mr. Netanyahu appears far less deterred by either foreign pressure or domestic frailty. Fighting in Gaza has slowed, allowing the Israeli military to focus on Hezbollah, while Mr. Netanyahu did not even consult with the United States before authorizing the strike on Friday, according to U.S. officials.

“King Bibi is back,” said Nachman Shai, a former cabinet minister, referring to Mr. Netanyahu by his nickname. “If you compare Bibi now to Bibi 10 months ago, he’s a different person. He’s full of confidence.”

The attack on Mr. Nasrallah followed Mr. Netanyahu’s similarly risky decisions to strike a group of senior Iranian generals in April; kill Hezbollah’s top military commander in July; assassinate Hamas’s political leader on the same night; detonate thousands of Hezbollah pagers and radios this month; and mount one of the most intense and deadliest bombardments in modern warfare last Monday in Lebanon.

These devastating blows have yet to translate into clear strategic gains. Israel’s main aim is to allow more than 60,000 displaced Israelis back to their homes near the border, but Hezbollah is still firing brief rocket barrages there, preventing Mr. Netanyahu from achieving that goal.

Still, his moves have defied — and, at least for now, undermined — warnings by allies and foes alike that an escalation risked setting off a broader regional war involving Iran, Hezbollah’s benefactor, and its other Middle Eastern proxies.

Instead, each attack significantly harmed Hezbollah without provoking unmanageable responses from the militia or Iran, at least for the time being. Hezbollah has not yet responded with an avalanche of long-range missile attacks that analysts and officials had predicted would overwhelm Israel’s air defenses and destroy its power grid and other key infrastructure. Daily life in Israel continued on Sunday morning while Hezbollah was in disarray.

Mr. Netanyahu’s sense of achievement could ebb quickly if Hezbollah or Iran does suddenly respond with much deadlier rocket strikes, Mr. Shai said.

“But for the time being,” he said, “Bibi feels at the height of his power.”

Mr. Netanyahu’s growing confidence, some analysts say, has been partly fostered by the Biden administration’s reluctance to rein him in at earlier stages in the war.

Since October, President Biden and his aides have sometimes criticized Mr. Netanyahu’s government for the conduct of its campaign in Gaza, for failing to conclude a cease-fire deal with Hamas and for being too slow to send aid to Gazans. The United States also successfully deterred the planned attack on Beirut, Lebanon’s capital, last October.

But apart from briefly freezing one shipment of arms, Washington has rarely followed its criticism with practical consequences, continuing to provide Mr. Netanyahu’s government with diplomatic cover at the United Nations and billions of dollars’ worth of arms. Israel has strong bipartisan support in the United States, with both Democratic and Republican leaderships wary of criticizing Israeli policy, particularly in the run-up to the presidential election.

“Netanyahu feels he can continue manipulating them because, other than expressing their dissatisfaction, they’re doing nothing,” said Alon Pinkas, an analyst and former Israeli consul-general in New York.

“It’s worsened or intensified as we got closer to the U.S. election,” Mr. Pinkas said, adding that Mr. Biden seemed wary of taking any measure that might damage Vice President Kamala Harris’s chances of defeating former President Donald J. Trump in November.

Mr. Netanyahu’s moves also occurred against the backdrop of growing domestic pressure to act against Hezbollah.

The conflict between Israel and the Lebanese militia began during Israel’s occupation of south Lebanon in the 1980s. This round of fighting started last October, when Hezbollah began firing on Israeli positions in solidarity with Hamas, which had just raided Israel. The Israeli military fired back, leading to a low-intensity border war that both sides have so far avoided turning into an all-out ground conflict.

Still, the fighting displaced hundreds of thousands of people on either side of the border, including more than 60,000 in northern Israel. And the plight of those displaced Israelis led to growing calls for the prime minister to authorize a more decisive military campaign, including from a far-right party that holds the balance of power in Mr. Netanyahu’s fragile coalition government.

The day before the strike on Mr. Nasrallah, Itamar Ben-Gvir, the leader of that party, threatened to quit the government if Mr. Netanyahu agreed to a truce with Hezbollah instead of defeating it by force.

“When your enemy is on his knees, you do not allow him to recover,” Mr. Ben-Gvir said in a statement.

Some analysts also believe Mr. Netanyahu was spurred by a desire to atone for his government’s failure to prevent Hamas’s atrocities last October. The attack on Oct. 7 was the deadliest day of war in Israel’s history, ruining Mr. Netanyahu’s self-image as the guardian of Israel’s security. For years, Mr. Netanyahu had sought to contain Hamas instead of seeking its ouster, facilitating a deal with Qatar that helped the group survive financially, making it easier for Hamas to prepare for the surprise attack.

Mr. Netanyahu is “convinced that the only way to absolve himself, potentially, for Oct. 7 is to do something spectacular in Lebanon,” Mr. Pinkas said.

Others say that Mr. Netanyahu has long been wary of military adventurism. On Sunday morning, Israeli columnists speculated that he was in fact reluctantly cajoled into action by the military and intelligence leaders who masterminded and promoted the attacks on Hezbollah, as well as by fortuitous circumstances.

For example, the decision to explode hundreds of Hezbollah pagers this month was expedited by the fear that the militia was about to discover that the devices were compromised. That forced Mr. Netanyahu to choose between using the method immediately or losing it forever.

Just a day earlier, Mr. Netanyahu had been considering whether to fire the defense minister who oversaw the operation, Yoav Gallant, before postponing that move on the afternoon of the attack. For some, that chaotic dynamic created the impression that Mr. Netanyahu was making last-minute moves rather than enacting a carefully planned strategy.

Past Israeli leaders may have been swifter to act, according to Michael Stephens, an expert on the Middle East at the Royal United Services Institute, a London-based foreign affairs research group.

“The situation in the north is something no Israeli leader would have tolerated,” Mr. Stephens said. “Standing firm against international pressure while aggressively pursuing Israel’s security interests is just very Israeli. It’s not uniquely Bibi.”

Whatever his prior motivations, the risk now for Mr. Netanyahu is that he becomes hubristic, pursuing even grander military aims that ultimately backfire, analysts said.

In particular, Mr. Netanyahu faces calls to invade southern Lebanon and destroy the group’s border fortifications, which threaten Israeli communities close to Lebanon. Such a move could capitalize on Hezbollah’s weakness, but it also risks sucking Israel’s infantry into an unwinnable ground war on unfamiliar enemy territory.

Despite its losses, Hezbollah has yet to collapse. It could still claw back the initiative with support from Iran.

“These are all shifting moments,” said Itamar Rabinovich, a former Israeli ambassador to Washington. “What looks good today may not look good tomorrow.”

Victories in Lebanon will also have little direct effect on either the negotiations between Israel and Hamas for a cease-fire and hostage release deal in Gaza, or the fighting on the ground there. Israeli soldiers have decimated Hamas but are struggling to deliver a winning blow. The remaining Hamas leaders are believed to be surrounded by hostages, making them difficult to attack and conclusively defeat.

And the killing of Lebanese leaders in Lebanon will not resolve Israel’s longest-running challenge: its conflict with the Palestinians, who still seek a sovereign state regardless of Mr. Netanyahu’s moves against Hezbollah.

“Israeli governments have been carrying out assassinations for decades,” wrote Ayman Odeh, a Palestinian Israeli lawmaker, in a social media post after Mr. Nasrallah’s assassination. “It did not promote security and did not stop any war,” he added.

Ronen Bergman contributed reporting.

At least 170 people have died in Nepal after days of unceasing rain caused heavy flooding and triggered major landslides around the country, including in the densely populated region around Kathmandu, the capital.

The monsoon rains destroyed hundreds of homes and swept away bridges, cut off power and left downed trees as rescuers struggled to reach people, some of whom were trapped under debris while others were stranded on rooftops.

By late Saturday, the rains had lessened in intensity, allowing rescue workers to use helicopters and expand their search to more remote areas in the Dhading and Dolakha districts. More than 3,600 people have been rescued so far, but with more than 100 injured and dozens still missing, government officials said they expected the death toll to rise.

Nepal’s prime minister, K.P. Sharma Oli, who was in the United States attending the U.N. General Assembly meeting, urged Nepalis to have patience, saying on social media that the rains would subside soon.

“I’m preparing to return,” Mr. Oli said. “Let’s collaborate for rescue in the time of disaster.”

Nepal, the home of Mount Everest, is prone to landslides and floods because of its mountainous terrain and heavy monsoons. But the warming climate has made weather events more dangerous and deadly, causing frequent flooding from melting glaciers. Climate change has also intensified rainfall. At the same time, rapid development and haphazard construction have added to the risk that lives will be lost in natural disasters.

On Saturday afternoon, Satrudhan Kumar Mahato, a police inspector, reached a remote two-story house made of mud and stone whose residents were trapped in the Dolakha district, about three hours from Kathmandu. When Mr. Mahato and his team finally reached the house, they found three members of one family dead and a young child crying next to his dead mother, Mr. Mahato said.

“He was lying under the bed and plywood,” Mr. Mahato said. “I carefully removed the plywood of the bed and recovered him.” The child was then rushed to a hospital.

On Sunday, Mr. Mahato and other police officers continued their search-and-rescue operations, unearthing bodies from damaged houses. More than 5,000 police personnel equipped with helicopters, rafts, ropes and vehicles had been deployed.

After retrieving 14 bodies from a small bus that was buried by a landslide late Saturday night in the Dhading district, police officers located another buried bus and a van on Sunday, said Shailendra Thapa, a deputy armed police force superintendent. They retrieved 17 more bodies on Sunday, Mr. Thapa said.

The economic toll on Nepal is likely to be severe. Roads linking Kathmandu to other cities have been damaged, curtailing the transport of essential goods, from food to petroleum.

As many as 16 hydropower projects have sustained damage, forcing the country to import power from India, according to Nepal’s national news agency. Some parts of the country remained dark, and the disrupted power supply also curtailed internet service in Kathmandu and other cities.

Over almost a year of war in the Middle East, major powers have proved incapable of stopping or even significantly influencing the fighting, a failure that reflects a turbulent world of decentralized authority that seems likely to endure.

Stop-and-start negotiations between Israel and Hamas to end the fighting in Gaza, pushed by the United States, have repeatedly been described by the Biden administration as on the verge of a breakthrough, only to fail. The current Western-led attempt to avert a full-scale Israeli-Hezbollah war in Lebanon amounts to a scramble to avert disaster. Its chances of success seem deeply uncertain after the Israeli killing of Hassan Nasrallah, the longtime leader of Hezbollah, on Friday.

“There’s more capability in more hands in a world where centrifugal forces are far stronger than centralizing ones,” said Richard Haass, the president emeritus of the Council on Foreign Relations. “The Middle East is the primary case study of this dangerous fragmentation.”

The killing of Mr. Nasrallah, the leader of Hezbollah over more than three decades and the man who built the Shiite organization into one of the most powerful nonstate armed forces in the world, leaves a vacuum that Hezbollah will most likely take a long time to fill. It is a major blow to Iran, the chief backer of Hezbollah, that may even destabilize the Islamic Republic. Whether full-scale war will come to Lebanon remains unclear.

“Nasrallah represented everything for Hezbollah, and Hezbollah was the advance arm of Iran,” said Gilles Kepel, a leading French expert on the Middle East and the author of a book on the world’s upheaval since Oct. 7. “Now the Islamic Republic is weakened, perhaps mortally, and one wonders who can even give an order for Hezbollah today.”

For many years, the United States was the only country that could bring constructive pressure to bear on both Israel and Arab states. It engineered the 1978 Camp David Accords that brought peace between Israel and Egypt, and the Israel-Jordan peace of 1994. Just over three decades ago, Prime Minister Yitzhak Rabin of Israel and Yasir Arafat, the chairman of the Palestine Liberation Organization, shook hands on the White House lawn in the name of peace, only for the fragile hope of that embrace to erode steadily.

The world, and Israel’s primary enemies, have since changed. America’s ability to influence Iran, its implacable foe for decades, and Iran’s proxies like Hezbollah is marginal. Designated as terrorist organizations in Washington, Hamas and Hezbollah effectively exist beyond the reach of American diplomacy.

The United States does have enduring leverage over Israel, notably in the form of military aid that involved a $15 billion package signed this year by President Biden. But an ironclad alliance with Israel built around strategic and domestic political considerations, as well as the shared values of two democracies, means Washington will almost certainly never threaten to cut — let alone cut off — the flow of arms.

The overwhelming Israeli military response in Gaza to the Oct. 7 Hamas massacre of Israelis and its seizure of some 250 hostages has drawn mild reprimands from Mr. Biden. He has called Israel’s actions “over the top,” for example. But American support for its embattled ally has been resolute as Palestinian casualties in Gaza have risen into the tens of thousands, many of them civilians.

The United States, under any conceivable presidency, is not about to desert a Jewish state whose existence had been increasingly questioned over the past year, from American campuses to the streets of the very Europe that embarked on the annihilation of the Jewish people less than a century ago.

“If U.S. policy toward Israel ever changed, it would only be at the margins,” Mr. Haass said, despite the growing sympathy, especially among young Americans, for the Palestinian cause.

Other powers have essentially been onlookers as the bloodshed has spread. China, a major importer of Iranian oil and a major supporter of anything that might weaken the American-led world order that emerged from the ruins in 1945, has little interest in donning the mantle of peacemaker.

Russia also has scant inclination to be helpful, especially on the eve of the Nov. 5 election in the United States. Reliant on Iran for defense technology and drones in its intractable war in Ukraine, it is no less enthused than China over any signs of American decline or any opportunity to bog America down in a Middle Eastern mire.

Based on his past behavior, the potential return to the White House of former President Donald J. Trump is probably seen in Moscow as the return of a leader who would prove complaisant toward President Vladimir V. Putin.

Among regional powers, none is strong enough or committed enough to the Palestinian cause to confront Israel militarily. In the end, Iran is cautious because it knows the cost of all-out war could be the end of the Islamic Republic; Egypt fears an enormous influx of Palestinian refugees; and Saudi Arabia seeks a Palestinian state but would not put Saudi lives on the line for that cause.

As for Qatar, it funded Hamas with hundreds of millions of dollars a year that went in part to the construction of a labyrinthine web of tunnels, some as deep as 250 feet, where Israeli hostages have been held. It enjoyed the complicity of Prime Minister Benjamin Netanyahu, who saw Hamas as an effective way to undermine the Palestinian Authority in the West Bank and so undercut any chance of peace.

The disaster of Oct. 7 was also the culmination of the cynical manipulation, by Arab and Israeli leaders, of the Palestinian quest for statehood. A year on, nobody knows how to pick up the pieces.

So in their annual pilgrimage, world leaders troop to the meeting of the General Assembly of the United Nations, where the Security Council is largely paralyzed by Russian vetoes over any Ukraine-related resolutions and American vetoes over Israel-related resolutions.

The leaders listen to Mr. Biden depict, yet again, a world at an “inflection point” between rising autocracy and troubled democracies. They hear the U.N. secretary general, António Guterres, deplore the “collective punishment” of the Palestinian people — a phrase that incensed Israel — in response to the “abhorrent acts of terror committed by Hamas almost a year ago.”

But Mr. Guterres’s words, like Mr. Biden’s, seem to echo in the strategic vacuum of an à la carte world order, suspended between the demise of Western domination and the faltering rise of alternatives to it. The means to pressure Hamas, Hezbollah and Israel all at once — and effective diplomacy would require leverage over all three — do not exist.

This unraveling without rebuilding has precluded effective action to stop the Israel-Gaza war. There is no global consensus on the need for peace or even a cease-fire. In the past, war in the Middle East led to soaring oil prices and tumbling markets, forcing the world’s attention. Now, said Itamar Rabinovich, a former Israeli ambassador to the United States, “the attitude is, ‘OK, so be it.’”

Absent any coherent and coordinated international response, Mr. Netanyahu and Yahya Sinwar, the Hamas leader and a mastermind of the Oct. 7 attack, face no consequences in pursuing a destructive course, whose endpoint is unclear but which will certainly involve the loss of more lives.

Mr. Netanyahu has shunned a serious American effort to bring about the normalization of relations with Saudi Arabia, perhaps the most important country in the Arab and Islamic world, because its price would be some serious commitment to the establishment of a Palestinian state, the very thing he has devoted his political life to preventing.

Mr. Netanyahu’s interest in prolonging the war to sidestep a formal reprimand for the military and intelligence failures that led to the Oct. 7 attack — a catastrophe for which the buck stopped on the prime minister’s desk — complicates any diplomatic efforts. So does his attempt to avoid facing the personal charges of fraud and corruption brought against him. He is playing a waiting game, which now includes offering little or nothing until Nov. 5, when Mr. Trump, whom he considers a strong ally, may be elected.

Israeli families who send their children to war do not know how committed their commander in chief is to bringing those young soldiers home safely by seizing any viable opportunity for peace. This, many Israelis say, is corrosive to the soul of the nation.

As for Mr. Sinwar, the Israeli hostages he holds give him leverage. His apparent indifference to the immense loss of Palestinian life in Gaza affords him considerable sway over world opinion, which has progressively turned against Israel as more Palestinian children are killed.

In short, Mr. Sinwar has little reason to change course; and, in what Stephen Heintz, the president of the Rockefeller Brothers Fund philanthropic organization, has called “the age of turbulence,” the world is not about to change that course for him.

“The institutions that have guided international relations and global problem-solving since the mid-20th century are clearly no longer capable of addressing the problems of the new millennium,” Mr. Heintz wrote in a recent essay. “They are inefficient, ineffective, anachronistic, and, in some cases, simply obsolete.”

That, too, has been a lesson of the year since Hamas struck.