At exactly 1 p.m. on Oct. 7, 2023, Israel’s military leadership issued an order that unleashed one of the most intense bombing campaigns in contemporary warfare.

Effective immediately, the order granted mid-ranking Israeli officers the authority to strike thousands of militants and military sites that had never been a priority in previous wars in Gaza. Officers could now pursue not only the senior Hamas commanders, arms depots and rocket launchers that were the focus of earlier campaigns, but also the lowest-ranking fighters.

In each strike, the order said, officers had the authority to risk killing up to 20 civilians.

The order, which has not previously been reported, had no precedent in Israeli military history. Mid-ranking officers had never been given so much leeway to attack so many targets, many of which had lower military significance, at such a high potential civilian cost.

It meant, for example, that the military could target rank-and-file militants as they were at home surrounded by relatives and neighbors, instead of only when they were alone outside.

In previous conflicts with Hamas, many Israeli strikes were approved only after officers concluded that no civilians would be hurt. Sometimes, officers could risk killing up to five civilians and only rarely did the limit rise to 10 or above, though the actual death toll was sometimes much higher.

On Oct. 7, the military leadership changed its rules of engagement because it believed that Israel faced an existential threat, according to a senior military officer who answered questions about the order on the condition of anonymity.

Hours earlier, Hamas-led terrorists had stormed into southern Israel, seizing towns and army bases, committing atrocities, firing thousands of rockets at civilian areas, killing up to 1,200 people and taking roughly 250 hostages. As Israelis battled Hamas fighters inside their borders, the officer said, Israel’s leaders also feared an invasion from the group’s allies in Lebanon and believed that they had to take drastic military action.

“All of the places where Hamas was deployed, in this city of evil, all of the places where Hamas has been hiding and operating from — we will turn them into rubble,” Prime Minister Benjamin Netanyahu of Israel said in a speech on Oct. 7.

An investigation by The New York Times found that Israel severely weakened its system of safeguards meant to protect civilians; adopted flawed methods to find targets and assess the risk of civilian casualties; routinely failed to conduct post-strike reviews of civilian harm or punish officers for wrongdoing; and ignored warnings from within its own ranks and from senior U.S. military officials about these failings.

The Times reviewed dozens of military records and interviewed more than 100 soldiers and officials, including more than 25 people who helped vet, approve or strike targets. Collectively, their accounts provide an unparalleled understanding of how Israel mounted one of the deadliest air wars of this century. Most of the soldiers and officials spoke on the condition of anonymity because they were barred from speaking publicly on a subject of such sensitivity. The Times verified the military orders with officers familiar with their content.

In its investigation, The Times found that:

• Israel vastly expanded the set of military targets it sought to hit in pre-emptive airstrikes, while simultaneously increasing the number of civilians that officers could endanger in each attack. That led Israel to fire nearly 30,000 munitions into Gaza in the war’s first seven weeks, more than in the next eight months combined. In addition, the military leadership removed a limit on the cumulative number of civilians that its strikes could endanger each day.

• On a few occasions, senior commanders approved strikes on Hamas leaders that they knew would each endanger more than 100 noncombatants — crossing an extraordinary threshold for a contemporary Western military.

• The military struck at a pace that made it harder to confirm it was hitting legitimate targets. It burned through much of a prewar database of vetted targets within days and adopted an unproven system for finding new targets that used artificial intelligence at a vast scale.

• The military often relied on a crude statistical model to assess the risk of civilian harm, and sometimes launched strikes on targets several hours after last locating them, increasing the risk of error. The model mainly depended on estimates of cellphone usage in a wider neighborhood, rather than extensive surveillance of a specific building, as was common in previous Israeli campaigns.

• From the first day of the war, Israel significantly reduced its use of so-called roof knocks, or warning shots that give civilians time to flee an imminent attack. And when it could have feasibly used smaller or more precise munitions to achieve the same military goal, it sometimes caused greater damage by dropping “dumb bombs,” as well as 2,000-pound bombs.

The air campaign was at its most intense during the first two months of the war, when more than 15,000 Palestinians were killed — or roughly a third of the overall toll, according to the Gazan health ministry, which does not differentiate between civilians and combatants.

From November 2023 onward, amid a global outcry, Israel began to conserve ammunition and tighten some of its rules of engagement, including by halving the number of civilians who could be endangered when striking low-ranked militants who posed no imminent threat. But the rules remain far more permissive than before the war. Since those early weeks, more than 30,000 Palestinians have been killed, and while Israel disputes the ministry’s figures, the total continues to climb.

Provided a summary of The Times’s findings, the Israeli military acknowledged that its rules of engagement had changed after Oct. 7 but said in a 700-word statement that its forces have “consistently been employing means and methods that adhere to the rules of law.”

The changes were made in the context of a conflict that is “unprecedented and hardly comparable to other theaters of hostilities worldwide,” the statement added, citing the scale of Hamas’s attack; efforts by militants to hide among civilians in Gaza; and Hamas’s extensive tunnel network.

“Such key factors,” the statement said, “bear implications on the application of the rules, such as the choice of military objectives and the operational constraints that dictate the conduct of hostilities, including the ability to take feasible precautions in strikes.”

The relatives of Shaldan al-Najjar, a senior commander in a militia allied with Hamas that joined the Oct. 7 attacks, were among the first casualties of Israel’s loosened standards.

When the military struck his home in a war nine years earlier, it took several precautions to avoid civilian harm — and no one was killed, including Mr. al-Najjar.

When it targeted him in this war, it killed not just him but also 20 members of his extended family, including a 2-month-old baby, according to his brother Suleiman, who lived in the home that was hit and witnessed the immediate aftermath. Some relatives were blown from the building. His niece’s severed hand was found in the rubble.

“Blood was splattered all over the neighbor’s wall — as though some sheep had just been slaughtered,” the brother recalled.

Israel, which has been accused of genocide in a case before the International Court of Justice, says it complies with international law by taking all feasible precautions to minimize civilian casualties, often by ordering evacuations of whole cities before strikes, and by dropping leaflets over neighborhoods and posting online maps about imminent operations.

Israel says that Hamas’s military strategy makes bloodshed more likely. The group embeds itself in the civilian population, firing rockets from residential areas, hiding fighters and weapons inside homes and medical facilities, and operating from underground military installations and tunnels.

Unlike Hamas, which fires rockets indiscriminately at civilian areas, Israel and all Western armies operate under a multilayered oversight system that assesses the legality of planned strikes. Each attack plan is usually meant to be analyzed by a group of officers, which often includes a military lawyer who can advise on whether strikes might be unnecessary or unlawful.

To comply with international law, officers overseeing airstrikes must conclude that the risk of civilian casualties is proportional to the target’s military value, and take all feasible precautions to protect civilian life. But officers exercise significant discretion because the laws of armed conflict are vague about what counts as a feasible precaution or an excessive civilian toll.

After the shock of the Oct. 7 attack, a dozen officers recalled, some Israeli officers involved in the counteroffensive became less stringent about adhering to military protocol. While some commanders tried hard to maintain standards, five senior officers used the same phrase to describe the prevalent mood inside the military: “harbu darbu.”

It is an expression derived from Arabic and widely used in Hebrew to mean attacking an enemy without restraint.

Why Civilians Were at Higher Risk

The Israeli military first targeted Shaldan al-Najjar during the war in August 2014. He was a senior commander in Palestinian Islamic Jihad, which had conducted suicide bombings and rocket attacks against Israel for decades.

Before that strike in Deir al Balah, central Gaza, the air force gave his neighbors three chances to escape, according to his brother Suleiman.

Israeli officers called one neighbor, and then another, with warnings of an upcoming strike on a nearby target that the military did not identify. Then the military dropped a small projectile on the house, what it calls a “roof knock,” standard practice then before strikes on targets believed to hold ammunition or tunnel entrances. That was enough for everyone, including Shaldan al-Najjar, to escape unharmed.

But seven hours after Hamas attacked Israel last year, the order from Israel’s high command made roof knocks optional. In practice this meant the procedure was rarely used, officers said.

There were no warnings before an Israeli fighter jet fired at Shaldan al-Najjar on the evening of Oct. 10, 2023, as he visited his siblings’ home. The explosion killed Mr. al-Najjar, along with his stepmother, four children, a younger brother, a sister-in-law, 13 nephews and nieces, including the 2-month-old baby boy, named Zein, and at least one neighbor, according to records compiled by Gaza’s health authorities.

The Israeli military confirmed that it had been targeting a member of Islamic Jihad, but declined to release more information.

Under Israeli military protocols, there are four categories of risk for civilian casualties: Level Zero, which forbids soldiers to put any civilians at risk; Level One, which allows up to five civilian deaths; Level Two, which allows up to 10; and Level Three, which allows up to 20 — and became the standard on Oct. 7.

Suddenly, officers could decide to drop one-ton bombs on a vast array of military infrastructure — including small ammunition stockpiles and rocket factories — as well as on all Hamas and Islamic Jihad fighters. The definition of a military target included lookouts and money changers suspected of handling Hamas’s funds, as well as the entrances to the group’s underground tunnel network, which were often hidden in homes.

Authorization from senior commanders was required only if the target was too close to a sensitive site, like a school or health facility, though such strikes were regularly approved too.

The effect was swift. Airwars, a London-based conflict monitor, documented 136 strikes that each killed at least 15 people in October 2023 alone. That was almost five times the number the group has documented during any comparable period anywhere in the world since it was founded a decade ago.

Strikes that endangered more than 100 civilians were occasionally permitted to target a handful of Hamas leaders, as long as senior generals or sometimes the political leadership approved, according to four Israeli officers involved in target selection. Three of them said those targeted included Ibrahim Biari, a senior Hamas commander killed in northern Gaza in late October, in an attack that Airwars estimated killed at least 125 others.

Another order, issued by the military high command at 10:50 p.m. on Oct. 8, provides a sense of the scale of civilian casualties deemed tolerable. Strikes on military targets in Gaza, it said, were permitted to cumulatively endanger up to 500 civilians each day.

Military officials characterized the order as a precautionary measure intended to cap the number of strikes that could take place each day. A scholar at West Point consulted by The Times, Prof. Michael N. Schmitt, said it risked being construed by mid-ranking officers as a quota that they had to reach.

In any case, the limit was removed two days later — allowing officers to sign off on as many strikes as they believed were legal. The Gazan authorities later reported occasional daily tolls of more than 500, but it was unclear how many were civilians or if their deaths had occurred over several days.

The risk to civilians was also heightened by the Israeli military’s widespread use of 1,000- and 2,000-pound bombs, many of them American-made, which constituted 90 percent of the munitions Israel dropped in the first two weeks of the war. By November, two officers said, the air force had dropped so many one-ton bombs that it was running low on the guidance kits that transform unguided weapons, or “dumb bombs,” into precision-guided munitions.

This forced pilots to rely on unguided and less accurate bombs, the officers said. They were also increasingly dependent on outdated Vietnam-era bombs that can fail to detonate, according to two U.S. military officials briefed on Israel’s arsenal.

The air force used the one-ton bomb to destroy whole office towers, two senior Israeli military officials said, even when a target could have been killed by a smaller munition.

While declining to comment on specific incidents, the Israeli military said that its “choice of munitions” was always governed by the rules of war. The senior military official said that heavy munitions were required to hit Hamas’s tunnels.

The Najjar family was struck by a precision-guided one-ton bomb — an American-made JDAM, according to a Times assessment of a guidance fin that the family said it had found in the rubble. The bomb completely destroyed their three-story building, flattening five apartments as well as a car workshop on the ground floor, according to the brother and two other surviving members of the family.

“After the dust and smoke cleared, I looked at my building,” said Suleiman al-Najjar, who said he survived because he was on his way back from the hospital. “There was no building.”

A Depleted Target Bank

Throughout the war, hundreds of Israeli intelligence officers spread across several military bases scrambled to find and strike new targets, relying on an automated surveillance system that enabled them to work exponentially quicker.

In earlier wars in Gaza, officers had typically worked their way through a “target bank” — a database of hundreds of militants and locations that already had been methodically researched and vetted. In this war, the air force raced through much of the list within days, 11 officers and officials said, putting intelligence officers under intense pressure to find new targets.

Many were encouraged to propose a certain number of targets each day, according to five officers.

Several elite intelligence units, officials said, were given more time to find small numbers of high-value targets, like senior Hamas political leaders and top military commanders. Other units focused on rocket launch sites and ammunition stores. One unit looked specifically for civilians who provided financial services to militant groups.

But most intelligence units, particularly those in infantry divisions preparing to invade Gaza, were given very little time to build a much longer list of targets, officials said. That mainly involved trying to locate tens of thousands of low-ranking militants.

Israel has long maintained databases, one of which was code-named “Lavender,” that list phone numbers and home addresses of suspected militants, according to 16 soldiers and officials. Israel also controls Gaza’s telecom networks, allowing it to tap and track Palestinian phones. By listening to calls made by phones associated with the militants, intelligence officers tried to work out where they were, officials said.

But the databases sometimes included outdated data, according to six officers, increasing the likelihood that officers would misidentify a civilian as a combatant. There were also too many calls for the officers to manually track.

To speed up the process, officers used artificial intelligence.

In recent years, the Israeli military had developed computing systems, one of which was known as “The Gospel,” that could automatically cross-reference information from several different sources, including phone conversations, satellite imagery and mobile phone signals.

In the chaotic opening weeks of the war, different intelligence units harnessed these automated computing systems in varied ways to triangulate data and locate militants.

One common method involved automatically cross-referencing the location of a phone with its owner’s home address. When a phone appeared to be in roughly the same place as an address linked to its owner, the system flagged and recorded the owner’s phone calls.

Arabic-speaking soldiers then listened to these calls to determine whether a wanted militant had been found. Some units used speech-to-text software to translate the conversations automatically.

The military said officers always verified the information provided by the automated systems and it denied that artificial intelligence was ever more than the starting point of a human-led verification process. But the amount of verification varied from unit to unit, according to at least eight officers.

Some officers said they would only confirm someone as a militant if they overheard the person speaking about their involvement in Hamas’s military wing.

In other units, three officers said, an individual was considered a confirmed militant if he was simply listed in Lavender. Details of that process were previously reported by +972, an Israeli-Palestinian news website; the Israeli military has denied that was military policy and said that any analyst who relied solely on Lavender would have been overruled by superiors.

Once officers were satisfied that they had confirmed a legal target, they would begin planning an attack, such as a missile strike if the target seemed to be staying the night at home, the soldiers said.

The first step was to gauge the civilian risk.

In the most rigorous version of that assessment, officers sometimes hacked a target’s phone handset to listen to the conversations taking place nearby, in order to build a better picture of whom he was with, according to three officers familiar with the process. In some cases, the hacking allowed officers to pinpoint the target’s location as well as which way he was facing, how many floors he had climbed and how many steps he had recently taken.

As an additional precaution, officers sometimes attempted to trace the phones of the buildings’ other known prewar residents — a laborious process that could take more than an hour.

But the military was pursuing so many targets that officers often lacked the time or resources for such sophisticated surveillance, particularly when tracking low-ranking militants early in the war, according to seven officials and soldiers.

Officers could still intercept calls and determine a phone’s rough location by checking which cellphone towers received its signals. That information was less precise — and it was more difficult to ascertain who was nearby.

Overlooked Civilians

In the absence of more accurate data, Israeli intelligence officers routinely used a simplistic model to estimate the number of civilians who might be killed in an airstrike, according to 17 soldiers and officials.

The military divided Gaza into 620 sectors, most the size of a few city blocks, and estimated the number of working phones in each using the signals received by cellphone towers. After comparing phone and Wi-Fi usage with prewar levels, the military then estimated the proportion of residents who remained in each sector.

To gauge the number of civilians inside a particular building, officers typically assumed that the building’s prewar residents had fled at the same rate as the surrounding neighborhood.

Even at its best, the model provided information that might be out of date by the time of an airstrike. The volume of attacks meant that there was often an hourslong gap between the assessment of civilian risk and the actual strike on the target, according to eight officers.

When the air force tried to kill a money changer connected to Islamic Jihad in mid-November 2023, for example, seven hours had passed since intelligence officers last checked where he was and who he was with, according to an official familiar with the attack. The strike killed two women — but the target survived because he was no longer there, according to the official and a second person familiar with the incident.

The model also suffered from fundamental flaws.

It relied, for example, on people having enough electricity to power their phones — and a working phone network. But power and network outages in Gaza often made that impossible.

The location of handsets also cannot be determined with complete accuracy based on phone signals; phones that seem to be in one neighborhood may be in an adjacent one. And the model also ignored how, during times of war, people often cluster together in large groups, three officers said.

Starting in November, senior officers in the American Joint Special Operations Command repeatedly raised concerns about the model’s accuracy with their Israeli counterparts, warning that it was leading to catastrophically imprecise assessments, according to the two senior U.S. military officials familiar with the conversations.

Some within the Israeli military also sounded the alarm. Throughout November and December, Israeli Air Force analysts urged colleagues to use more extensive drone surveillance to check for the presence of civilians, according to internal military assessments. Little to no action was taken, at least for several weeks, according to those assessments. The air force was supposed to recheck estimates of civilian presence but did not always do so.

Even when conducting after-action reviews, the military rarely tried to count how many civilians had been killed, making it almost impossible for officers to assess the model’s accuracy, according to 11 officers involved in target selection.

The Israeli military’s statement to The Times did not address questions about the model, but it said that in general the military’s methods “adhere to the rules of law, whether it be the choice of munitions or the use of digital technologies to support this effort.”

Israel’s strike on a residential street on the edge of Gaza City on Nov. 16, 2023, exemplified how inaccurate the model could be. The military told The Times in a statement that it was trying to destroy one of the many tunnels used by Hamas’s military wing. In the process, it hit a large house.

Before the war, 16 members of the extended Malaka family lived in the three-story building, according to two surviving brothers, Hazem and Nidal Malaka. After the war began, dozens of other relatives moved in, they said.

At the moment of the strike, 52 people — including Hazem and Nidal Malaka — were crammed into the bottom two floors. The brothers drew a family tree for The Times that detailed their names and backgrounds, and provided photographs of many of them. The oldest was the 64-year-old family patriarch, Jamal, and the youngest was his 2-year-old granddaughter, Sham.

By this point in the war, the surrounding neighborhood, Zeitoun, was largely depopulated. Israel’s formula for assessing the building’s occupancy, based on phone usage in the wider neighborhood, would have suggested there was only a handful of civilians left.

And several hours before the strike, phone reception was lost across Gaza, service providers announced at the time. That meant that a manual attempt to track the handsets of the building’s prewar residents may have suggested there was no one there at all.

The first reports of the strike emerged only after the network outage ended, three days later on Nov. 19.

By the brothers’ count, at least 42 people were killed and just 10 survived. Hazem Malaka said that most of them were not officially recorded as dead because the victims’ bodies were left trapped in the rubble instead of being taken to the nearest hospital where deaths are registered.

Hazem Malaka, 40, lost his pregnant wife, son and daughter. To the best of his knowledge, he said, their bodies still lie crushed “under three floors of concrete.”

Tightening the Reins

About two months ago, Israel struck a hospital compound in central Gaza where thousands of displaced Palestinians were sheltering. Several burned to death, including Shaaban al-Dalou, a 19-year-old university student, who was filmed flailing helplessly in his tent as the flames engulfed him.

Israeli officials blamed Hamas for the blaze, saying it likely occurred after an Israeli missile, targeting a Hamas command center, hit munitions that the group had stored in the hospital compound.

“All I wanted was for him to look at me one last time,” said Mr. al-Dalou’s father, Ahmed, as he recalled watching his son burn to death.

The attack occurred about 500 yards south of where the militant commander Shaldan al-Najjar was killed a year and four days earlier.

Still, the military has steadily used fewer munitions over the past 12 months, according to officers and records reviewed by The Times. The average number of munitions used by Israel each month in Gaza fell from a high of nearly 15,000 in October and November 2023 to less than 2,500 from February through May. (The Times was unable to verify the number of munitions fired since June.)

In relative terms, Israel has also tightened its rules of engagement.

On Nov. 5, 2023, the military leadership decreed that officers needed special permission to endanger more than 10 civilians in strikes on low-ranking militants who posed no imminent threat to Israeli infantry. By late January, officers needed special permission for nearly all such deadly strikes, except for those targeting the most senior Hamas commanders.

But the rules were still far looser than they were before Oct. 7.

Mid-ranking officers could still sign off on most strikes that endangered 10 civilians or less — a threshold far higher than the prewar norm.

And many strikes proved far deadlier.

In July, Israel fired several missiles at Hamas militants, including a top commander, Muhammad Deif, killing at least 57 people, according to Airwars.

Israeli officers have also acted with near impunity. Only two officers are known to have been fired for their role in the air campaign, after they oversaw a drone strike that killed several foreign aid workers whom the officers had confused for militants.

The military said that a panel appointed by the military chief of staff was investigating the circumstances of hundreds of strikes.

No one has been charged.

Abu Bakr Bashir, Johnatan Reiss and Aaron Boxerman contributed reporting.

The cartel operatives came to the homeless encampment carrying syringes filled with their latest fentanyl formula. The offer was simple, according to two men living at the camp in northwest Mexico: up to $30 for anyone willing to inject themselves with the concoction.

One of the men, Pedro López Camacho, said he volunteered repeatedly — at times the operatives were visiting every day. They watched the drug take effect, Mr. López Camacho said, snapping photos and filming his reaction. He survived, but he said he saw many others who did not.

“When it’s really strong, it knocks you out or kills you,” said Mr. López Camacho of the drugs he and others were given. “The people here died.”

This is how far Mexican cartels will go to dominate the fentanyl business.

Global efforts to crack down on the synthetic opioid have made it harder for these criminal groups to find the chemical compounds they need to produce the drug. The original source, China, has restricted exports of the necessary raw ingredients, pushing the cartels to come up with new and extremely risky ways to maintain fentanyl production and potency.

The experimentation, members of the cartels say, involves combining the drug with a wider range of additives — including animal sedatives and other dangerous anesthetics. To test their results, the criminals who make the fentanyl for the cartels, often called cooks, say they inject their experimental mixtures into human subjects as well as rabbits and chickens.

If the rabbits survive beyond 90 seconds, the drug is deemed too weak to be sold to Americans, according to six cooks and two U.S. Embassy officials who monitor cartel activity. The American officials said that when Mexican law enforcement units have raided fentanyl labs, they have at times found the premises riddled with dead animals used for testing.

“They experiment in the style of Dr. Death,” said Renato Sales, a former national security commissioner in Mexico. “It’s to see the potency of the substance. Like, ‘with this they die, with this they don’t, that’s how we calibrate.’”

To understand how criminal groups have adapted to the crackdown, The New York Times observed fentanyl being made in a lab as well as a safe house, and spent months interviewing several people directly involved in the drug’s production. They included nine cooks, three chemistry students, two high-level operatives and a recruiter working for the Sinaloa Cartel, which the U.S. government blames for fueling the synthetic opioid epidemic.

The people connected to the cartel spoke on the condition of anonymity for fear of retaliation.

One cook said he recently started mixing fentanyl with an anesthetic often used in oral surgery. Another said the best additive he had found was a sedative for dogs and cats.

Another cook demonstrated for Times reporters how to produce fentanyl in a cartel safe house in Sinaloa State, in northwest Mexico. He said that if the batch was too weak, he added xylazine, an animal tranquilizer known on the street as “Tranq” — a combination that American officials warn can be deadly.

“You inject this into a hen, and if it takes between a minute and a minute and a half to die, that means it came out really good,” the cook said. “If it doesn’t die or takes too long to die, we’ll add xylazine.”

The cooks’ accounts align with data from the Mexican government showing a rise in the use of fentanyl mixed with xylazine and other substances, especially in cities near the U.S. border.

“The illicit market gets much more benefit from its substances by cutting them with different things such as xylazine,” said Alexiz Bojorge Estrada, deputy director of Mexico’s mental health and addiction commission.

“You enhance it and therefore need less product,” said Ms. Bojorge, referring to fentanyl, “and you get more profit.”

U.S. drug researchers have also noticed a rise in what one called “weirder and messier” fentanyl. Having tested hundreds of samples in the United States, they found an increase in the variety of chemical compounds in fentanyl on the streets.

“It’s just a wild west of experimentation,” said Caleb Banta-Green, a research professor at the University of Washington School of Medicine, who helped coordinate the testing of more than 580 samples of drugs sold as fentanyl in Washington State this year.

He called it “absolute chaos.”

The Experiments

The synthetic opioids that reach American streets often begin in cartel labs, where precision is not always a priority, cooks say. They mix up vats of chemicals in rudimentary cook sites, exposing themselves to toxic substances that make some cooks hallucinate, wretch, pass out and even die.

The cartels are actively recruiting university chemistry students to work as cooks. One student employed by the cartel revealed that to test their formulas, the group brought in drug users living on the street and injected them with the synthetic opioid. No one has ever died, the student said, but there have been bad batches.

“We’ve had people convulse, or start foaming at the mouth,” the student said.

Mistakes by cooks were met with severe punishment, she added: Armed men locked the offenders in rooms with rats and snakes and left them there for long stretches with no food or water.

The cooks and high-level operatives described the Sinaloa Cartel as a decentralized organization, a collection of so many disparate cells that no single leader or faction had complete control over the group’s fentanyl production.

Some cooks said they wanted to create a standardized product that wouldn’t kill users. Others said they didn’t see the lethality of their product as a problem — but as a marketing tactic.

In a U.S. federal indictment against the sons of the notorious drug lord Joaquín Loera Guzmán (known as El Chapo) who lead a powerful faction of the Sinaloa Cartel, prosecutors said the group sent fentanyl to the United States even after an addict died while testing it in Mexico.

Instead of scaring people off, cartel members, drug users and experts say that many American users rush to buy a particularly deadly batch because they know it will get them high.

“One dies, and 10 more addicts are born,” said one high-level operative for the cartel. “We don’t worry about them.”

The Boss

The boss knew something was wrong when the hens stopped keeling over. He said he’d been in the drug business since he was 12, when he started apprenticing at a heroin processing site.

Now a soft-spoken 22-year-old, the boss said he taught himself how to produce illicit drugs by studying the older, more experienced men he worked with. Eventually, he started his own business with a friend.

The boss said his business grew so fast that soon he was running three fentanyl labs. The drug has made him millions, he said.

Every time he goes to one of his labs, he said he brings four or five rabbits from the local pet store. If the fentanyl his people make is potent enough, he has to inject and kill only one to be sure it is fit for sale.

Two pet store employees in Sinaloa, who spoke on the condition of anonymity for fear of retaliation from cartel members, confirmed that the cheapest rabbits are known to be purchased for drug testing.

The boss’s other test subjects are hens from a nearby ranch. Many fentanyl cooks test their product on chickens, according to the two U.S. Embassy officials.

Until recently, the boss said every time he injected the hens with fentanyl they would either die, fall over or stumble around as if they were drunk. All the locals knew not to eat the chickens or the eggs from the ranch.

But recently, the animals weren’t having a strong reaction to the drug, even though his process hadn’t changed.

His employees were logging the same hours at the same modest lab in the mountains, starting at 5 a.m. and sleeping there for days on end. They were working with the same equipment — laboratory shakers, trays, large containers and a blender to mix up the final product.

The boss said he eventually concluded that the culprit was a “very diluted” supply of the chemical ingredients from China. The result was a bunk product.

“It’s too weak,” he said.

To fix the problem, the boss first tried combining fentanyl with ketamine, a short-acting anesthetic, but said users didn’t like the bitter taste that came with smoking the mix. It worked much better to add procaine, he said, a local anesthetic often used to numb small areas during dental procedures.

When asked whether he felt guilty about producing a drug that causes mass death, the boss said all he was doing was giving his customers what they wanted.

“If there weren’t all those people in the United States looking to get high, we wouldn’t sell anything,” he said. “It’s their fault, not ours. We just take advantage of the situation.”

The Cook

One cook we spoke with said he got into the fentanyl business a few years ago to pay off growing debts. At first, the former shop owner regularly got sick from the exposure to the fumes. He said the armed cartel members in charge had no patience for it.

“You may throw up at the beginning when you start, and you take a quick break and take some air,” said the cook, but soon enough “one of them will scream at you to get back to work.”

A boss once shot him just because he didn’t answer a question quickly enough, he said, pulling up his shirt to reveal a stomach scar.

He is constantly experimenting with ways to make fentanyl stronger, tweaking his formula and testing it on his lab assistants, many of whom have become addicted in the process, he said. If the product comes out strong, he passes it on to his supervisors to try.

The cook said he knows all the improvisation adds up to an unpredictable product. Each batch he makes is different, he said, meaning clients who buy the exact same fentanyl pills may get wildly different doses from week to week.

He’s never fully disclosed his job to his family, simply saying he’s off to work and then returning weeks later with a lot of cash. He believes the money and the fear evident in his expression deter any questions.

“There is no retirement here,” the cook said, adding that the cartel would likely kill him for trying to stop. “There is just work and death.”

At a makeshift clinic in Sudan’s battle-torn capital, a determined young woman rushed to save fighters and civilians alike.

She had no formal medical training. But as beat-up cars skidded to a halt outside the clinic’s door, disgorging the wounded, she did her best to treat them — stanching gunshot wounds, changing dressings, improvising blood tests with her cellphone.

Drones buzzed overhead. Snipers perched on rooftops. Explosives struck the clinic, and more than once, the woman, Amal Abdelazeem, thought she was going to die.

The war has remade her. “I’m a different person now,” she said, days after escaping the city.

Hers was the generation that was supposed to save Sudan. They thronged the streets and toppled a dictator in 2019, in a moment of audacious hope that promised a sparkling future to wash away the decades of stale autocracy. Ms. Abdelazeem, then in college, attended one protest. “We needed a new Sudan,” she said.

But the old Sudan returned quickly, and with a vengeance. The civil war that erupted last year between rival military factions not only split a giant African nation in two — it also derailed an entire generation, forcing young Sudanese to make painful choices as they navigated a war that few wanted.

Democracy activists picked up guns to fight alongside the soldiers they once despised. Artists set up food kitchens. Lawyers collected rape testimony. Millions fled Sudan.

But millions more, like Ms. Abdelazeem, who is 26, had to stay. She was trapped in a neighborhood that had fallen to the Rapid Support Forces, or R.S.F., the fearsome paramilitary group that is battling Sudan’s military for control of the country. Such areas are the conflict’s blind spots, so dangerous that even local reporters dare not venture there.

She had no money to run, and the war quickly presented a series of excruciating choices. It split her family — one brother was detained by the R.S.F., while another brother joined them. It forced her to choose between food and safety.

And she felt buffeted between the two sides, patching up fighters while being targeted by them, viewed with suspicion at every turn.

One morning at a checkpoint, a young R.S.F. fighter brusquely demanded to know why Ms. Abdelazeem insisted on wearing a niqab, the face veil that showed only her eyes. Was she spying for the other side? He tugged the veil from her face.

Enraged, Ms. Abdelazeem grabbed the fighter’s rifle, turned it around and pointed it straight into his face.

“I wanted to shoot him,” she recalled, blinking through tears. “But I couldn’t.”

Saucepan Helmets

Ms. Abdelazeem knew what it was to struggle.

She had grown up on the western edge of the capital, Khartoum, where the urban sprawl blends into the desert, in a family of working-class strivers who prized education. She graduated with first-class honors in laboratory sciences in 2020.

After college, she also began to wear the niqab, a decision that horrified her mother. Ms. Abdelazeem said she had always been strong-willed. But she gave herself easily to stories, devouring thrillers, philosophy and internet culture that fed her restless curiosity.

She loved frothy American sitcoms like “Friends” — although she didn’t approve of how the characters slept around. She preferred the pop stars and television shows of South Korea, whose culture she saw as more innocent and sweet. She taught herself the rudiments of Korean from YouTube and got her first passport in 2022 in the hope of traveling to the country.

But a year later, war broke out, and those plans were shelved.

At first, she stayed out of it. Fighting was concentrated across the River Nile, in downtown Khartoum, and her neighborhood in Omdurman was relatively quiet.

But then government warplanes bombed an R.S.F. base nearby, scattering fighters across the area. They ransacked homes, stole cars and broke open a prison in search of recruits. Beggars were executed by fighters who accused them of spying for the military. When thunderous gunfire erupted outside her family’s home, she cowered under the kitchen table, gripping a stick against potential rapists. Her mother wore an upturned saucepan on her head to protect against bullets. “Ridiculous, I know,” Ms. Abdelazeem said, chuckling at the memory.

In fact, the joke was on the R.S.F., she said. It turned out that the fighters were firing in the air to celebrate reports they had killed Sudan’s military chief — which turned out to be wrong.

The war closed in on her family. Ms. Abdelazeem’s mother fell sick and died suddenly. They started to run out of money. She sold her laptop and phone, for a pittance, to an R.S.F. fighter. But he was killed before paying the full amount.

As she grew desperate, Ms. Abdelazeem heard about a job at a makeshift private clinic in an abandoned clothes factory near the front line. She took it.

“I figured it was better to die from bullets than from starvation,” she said.

The Clinic

A small team of medics ran the clinic, offering to help wounded fighters for money, and local residents for free. Most fighters arrived with gunshot wounds, Ms. Abdelazeem said, while some had been stabbed in disputes or injured in car crashes as they careened through empty streets.

A majority of the fighters in that area were Libyan, she said — one of numerous foreign contingents in a war that has drawn mercenaries from Africa, Russia, Ukraine and even Colombia. “They drank a lot,” she said.

She learned on the job, treating wounds and dispensing drugs, but also drew on her training to set up a laboratory for blood samples, improvising tests with a technique that used the flash on her cellphone camera. Many fighters had syphilis and other sexually transmitted infections, she discovered.

That clinic’s work turned it into a target for Sudan’s military, she said. When she went onto the roof in an effort to grab the weak cellphone signal, she removed her white lab coat to reduce the risk of being hit by drones firing bombs.

Nearly half of all hospitals in the capital area have been damaged in the war, targeted by both sides, according to a recent report from the Yale School of Public Health.

Sometimes, Ms. Abdelazeem earned as little as $2 a day. But she also found purpose in the work, especially when injured children were saved. A strong camaraderie developed among the besieged medics, driven by the adrenaline that comes from living on the edge.

“To be honest, it could be fun,” she said. After close calls, “it made us appreciate life.”

Brothers

To help feed the family, her 21-year-old brother, Yassin, took odd jobs. But that raised the suspicions of R.S.F. fighters, who beat and detained him three times, he said in an interview. Once, he escaped by ambushing an R.S.F. guard and throttling him. “I didn’t look back,” he said.

But another brother, Mohamed, 25, joined the R.S.F.

Mohamed had always been trouble, Ms. Abdelazeem said, and in the war fell in with a group of R.S.F. fighters who roamed their neighborhood. He was assigned to an internal R.S.F. unit charged with reining in the widespread car theft that made the group unpopular, she said.

Then Mohamed looted his own family’s home, she said, walking out with a fridge and a TV, brushing past his sister as she implored him to stop.

The violence drew dangerously close. The clinic pharmacist died, she recounted, after a bomb hit the bus she was traveling in. A friend who was a nurse said she was nearly raped by an R.S.F. commander. The clinic shut down after being struck by a volley of drone strikes.

One day, Ms. Abdelazeem was visiting another hospital when Libyan mercenaries rushed in carrying a seriously wounded fighter. A doctor did his best to save him. But after some minutes, one fighter, apparently believing his comrade could not survive, pulled out a gun and shot him dead.

“In the heart!” Ms. Abdelazeem said, crying softly and kneading her hands as she spoke. “You can’t kill someone just because there’s no hope,” she added. “Where is God in that?”

It was the final straw. Gathering up her last belongings and five family members, Ms. Abdelazeem boarded a bus for Port Sudan, 500 miles by road to the east. At a checkpoint, Sudanese Army personnel held up the bus while they interrogated her about the medicines in her bag, suspicious she had aided the other side.

Exiled to Casablanca

Perched on the Red Sea, Port Sudan is the Casablanca of Sudan’s war — a place where people from across Sudan blow in, seeking shelter or fortune or travel papers enabling them to flee the country as quickly as possible. The wealthier ones lounge by the sea in the evening, drinking coffee and dangling their feet in the Red Sea. But Ms. Abdelazeem and her family couldn’t afford any of that.

They found lodgings in a sweltering university hostel crammed with 1,500 displaced women and children. That’s where we found Ms. Abdelazeem a week after her family arrived, remonstrating loudly about the poor conditions. Fights regularly erupted between the women, who hailed from across Sudan’s ethnic and social divides, she said. Children played in dirty corridors. Flies buzzed in toilets. Food was scarce.

She had been reunited with an older sister at the hostel — a bittersweet moment because the sister had attempted suicide weeks earlier, following a difficult divorce.

They all had to move again in December, when the authorities shifted the dormitory residents to a tented camp a few miles away. On a video call, Ms. Abdelazeem offered a tour of the desolate encampment, which had a single toilet for 200 families.

She was grateful to be alive, even if her family had joined the sea of 11 million Sudanese displaced by the war.

If she had learned one thing, she said, it’s that were no good guys in war. Both sides committed numerous atrocities. Yet, she couldn’t bring herself to hate them, or even to root for one side.

“In the end, they’re all Sudanese,” she said. “I feel sorry for them.”

That included her brother, Mohamed, who days earlier had called, saying he had had enough of fighting in the war and wanted money to get out. She barely had enough to feed herself and her family members. Still, she clung to the idea of saving him.

“He’s stupid, I know,” she said. “He’s irresponsible, I know.”

But, she added, “He’s still my brother.”

Abdalrahman Altayeb contributed reporting from Port Sudan, Sudan.

The cast gathered in the recording studio, taking turns at the microphones as animated scenes from one of Japan’s most beloved television cartoons played on screens in front of them. Midori Kato, 85, was the only gray-haired head in the room. She closed her eyes, appearing to doze for a moment until it was her character’s turn. She stepped up to a microphone, her shoulders slightly stooped and her gnarled hands grasping the paper script.

But when she opened her mouth to speak, it was with a cheerful, slightly nasal twang: the voice of a 24-year-old stay-at-home mother. To generations of Japanese, she is Sazae-san, the titular character of the world’s longest-running animated television series.

Since “Sazae-san” began airing on Sundays at 6:30 p.m. in 1969, Ms. Kato has voiced the bossy but kind, absent-minded woman who is forever sheepish about some mishap. Ms. Kato was recently honored with a Guinness World Record for the longest career as a voice actor for the same character in an animated TV series. She is the only remaining member of the original cast, and its oldest.

“Sazae-san” still airs weekly on Fuji TV in its original time slot. It portrays the day-to-day antics of Sazae, her husband and 3-year-old son, along with her parents (voiced by actors much younger than Ms. Kato), her mischievous elementary-age brother and sweet younger sister. The three generations live in a suburban house in Tokyo, mostly frozen in the staunchly traditional time period of the earliest episodes. There is even a phrase, “Sazae-san syndrome,” referring to the Sunday night blues before the workweek begins.

The characters, who never age, are named after seafood products. Sazae (a mollusk that is a culinary delicacy in Japan) has maintained the same distinctive tripartite hairstyle for 55 years. The characters make calls on rotary phones or from telephone booths, and plot points often turn on missed communication that would not occur in the era of texting.

The show’s family dynamics and gender roles remain patriarchal. Neither Sazae nor her mother works outside the home, while her father and husband commute to distant offices, returning late and frequently drunk. The women do all the housework, child care and cooking, while the men largely wait to be served.

Ms. Kato, who was widowed three years ago and has no children, said the family structure in the show was familiar from her own childhood.

She grew up in suburban Tokyo in a family where “children were not supposed to pick up our chopsticks until our father did so.” Her father always bathed first, and “when someone left a newspaper open on the table, we were strictly scolded.”

Although the show’s characters have remained largely static for more than half a century, Ms. Kato still enjoys the two-hour recording sessions in a Tokyo studio every week. “The stories are funny, aren’t they?” she said during an interview after a recent taping. “So I never get bored. Never.”

Shunichi Yukimuro, a screenwriter who has written for the series for about 45 years, said the producers insist that the show maintain its period setting. He recalled when a younger writer put in a scene showing Sazae asking her husband to pick up clothes from a dry cleaner. That did not work, Mr. Yukimuro said, because in the 1960s, “it would be totally unacceptable for a family with two full-time housewives” to ask a man to do such a task.

In a country where nearly a third of the population is 65 or older, the show attracts a loyal — albeit shrinking — audience.

For elderly viewers, “death is the worst thing they are afraid of,” said Ms. Kato. “Old women say, ‘This is good! The characters live forever.’”

The show’s popularity peaked in the late 1970s, when it was the No. 1 cartoon on broadcast television in Japan and 40 percent of television-owning households in the country’s central region tuned in. Now, that figure fluctuates around 6 or 7 percent, amid a general decline in appointment-television watching.

“Sazae-san’s” gender roles are in some ways consistent with entrenched values and economic incentives that remain in Japan.

Mothers still perform far more housework and child care than fathers. Married couples must legally share the same surname, with wives much more likely than husbands to take their spouse’s last name.

“This kind of basic gender contract has not changed,” said Taotao Matsui, a professor of marketing at Rissho University in Tokyo. Japan’s tax system, in which nonworking spouses of full-time salaried employees can earn a pension, is “based on the Sazae-san model.”

Society has moved on in some ways: Women are much more likely to work outside the home. Many women choose not to marry or have children. Few suburban families currently live in multigenerational homes, and grandparents often see their grandchildren only on holidays.

For loyal fans, “Sazae-san” has “become a time capsule,” said Deborah Shamoon, associate professor of Japanese studies at the National University of Singapore. “It’s become a rosy view of how things used to be.”

The producers have made some concessions to modernity. Skytree, a tower that opened in Tokyo in 2012, looms on the horizon, and the Summer Olympics, held in 2021, appeared in the world of the show.

If Namihei, the father, wants some tea, he no longer barks “give me tea!” to his wife, Fune, but asks, “may I please have some tea” or even occasionally serves himself, said Hiroshi Namie, 67, a screenwriter.

Mr. Namie said he wished he could add some minor characters who were working mothers or unmarried women. “But it is a very high hurdle,” he said.

The television series is based on a comic strip that ran in two newspapers from 1946 to 1975. The cartoonist, Machiko Hasegawa, who died in 1992, was the first woman to pen a regular comic strip — or manga — in a daily Japanese newspaper, and the first in Japan to have her work adapted for television.

The early comics portrayed the hardships of life after World War II, when poverty-stricken Japanese lined up for rice rations or shopped on the black market. Sazae was a confident, single young woman unafraid to speak her mind.

By the time the television series aired, Sazae’s independence was sanded down and she was married to a salaried office worker and was the mother of a toddler. The family had become firmly middle-class.

Ms. Kato was hired as the youngest member of the “Sazae-san” cast. She said she got the job because of her “bouncing, cheerful, clean voice.”

Directors, she said, warned that they didn’t want her voice to sound “sexy” if the pitch dropped as she aged. She said she doesn’t drink or smoke, or go out late at night. Taxi drivers occasionally recognize her voice.

Ms. Kato has outlasted many other cast members. Last year the actress who voiced Tara, Sazae’s son, died at age 87.

Michiko Nomura, 86, voiced the character of Wakame, Sazae’s younger sister, for three decades until she retired in 2005. Ms. Nomura said her voice deepened with age, and she decided she could no longer play an 8-year-old girl. But she predicted Ms. Kato would continue “as long as she is healthy and alive.”

During a recent recording, Ms. Kato was sharp enough to notice that in a scene where the script called for Sazae to grunt, the animated character appeared gripping a pencil in her mouth. The director told her it was fine to take poetic license. Ms. Kato leaned into the microphone. “Huh, huh, huh!” she said vigorously, matching perfectly with the animated character’s movements as Sazae scrambled to pin down paper notes tossed by the wind.

Ryusuke Hikawa, a professor of Japanese animation technology and cultural studies at Meiji University, said the show gives people living in uncertain times “a sense of security.”

“It’s a big family whose members often quarrel and are a little clumsy but live happily together,” he said. “It’s inevitable that the expiration date will eventually come.”

Ms. Kato herself feels wistful about the world portrayed in the show. She used to live near a nursery school, she said, and observed children crying as their working mothers dropped them off in the morning. As someone who never had children herself, she said, after her husband died, “living alone is tough.”

The wave surged and rushed. It sent water as high as 160 feet slamming onto land with a force far outstripping that of an atomic bomb. When the tsunami inundated the coasts of more than a dozen Indian Ocean nations on Dec. 26, 2004, about 230,000 people lost their lives. Entire communities were erased. It was the deadliest tsunami in recorded history.

No one was immune to the giant wave, which was triggered by a 9.1 magnitude earthquake off the coast of the Indonesian island of Sumatra. Among the dead were fishermen, vacationers, sports stars and a prince.

The brunt of the tsunami was felt in the Indonesian province of Aceh, where 170,000 people perished. Sri Lanka, India and Thailand were devastated, too. More than a thousand miles apart, across the Indian Ocean, hundreds of coastal communities were united in their grief, and in facing years of rebuilding and regrouping.

Indonesia

Sri Lanka

India

Thailand