Residents of Sanaa, Yemen’s capital, after a Saudi-led airstrike in April. Photograph by Hani Mohammed / AP

In 1994, I took my mother on a vacation to Yemen, the most remote and populous corner of the Arabian peninsula. We landed, by ship, at the port city of Mukalla, once a major trading post between Africa and India. Whitewashed Arabesque buildings, with thick carved doors, stretched around the bay. Raw mountains loomed in the background. In the nineteen-thirties, the British explorer Freya Stark embarked from Mukalla for her journey into Arabia’s hinterland, and wrote of the “never-ending delight” of the city’s shoreline:

Acres of small flat silver fish with blue backs, laid out in rows like bedded plants, were strewn there in the sun: they dry for six days and are then stacked in heaps for the camels to feed on. They are caught in a circular net of small meshes, about 1 cm. square, thrown by a man who stands submerged to the waist beyond the breaking waves.

Today, Yemen is imploding. Al Qaeda in the Arabian Peninsula is seizing territory on the periphery. Last month, its forces seized Mukalla, now a city of some two hundred thousand. They emptied the prison, looted the provincial branch of the Central Bank, and stripped the local military base of arms and tanks. Mukalla’s airport became the first to fall under control of an Al Qaeda franchise anywhere.

My mother and I had flown out of that airport deep into the Hadramawt, the largest province in Yemen, famous for its frankincense and exotic architecture. Freya Stark dubbed the interior city of Shibam the “Manhattan of the Desert” because of its mud-brick skyscrapers that rise to eleven stories.

Mother and I decided to keep a joint trip journal. “The architecture in the Hadramawt region, which used to be part of socialist South Yemen until the north and south merged in 1990, often looked like three- and four-story fortresses,” we wrote one day. “Several generations of families live together, with various floors having distinct functions.” The patterns of human settlements were different from anything we had read about anywhere else. “Yemen,” we concluded, “is the closest you can come to knowing what it’s like to land on another planet.”

Yemenis have survived in formidable deserts and desolate mountains for millennia, but the country, which is four times the size of Alabama, is still trapped in a tribal clan-and-dagger past that has intensified in the years since unification, in 1990, because of legitimate grievances, petty feuds, cycles of vengeance, and political greed. Yemen’s sectarian splits have more to do with territory and dispersal of the treasury than with theology. Tensions have also erupted over water shortages that are so chronic that the government considered relocating the capital.

In our journal, we wrote of Sanaa, the capital: “Taxi drivers all wore djambias, or curved daggers, protruding from their belts, and they were all chewing gargantuan wads of qat, a mild stimulant narcotic which made their cheeks bulbous—and their driving wild.” In the afternoons, wandering through souq alleyways or historic sites, we saw groups of men squatting on the streets for hours at a stretch chewing the green leaves into oblivion. Some ninety per cent of Yemeni men, at least half the women, and up to twenty per cent of children still chew qat, according to the World Health Organization and the World Bank, despite campaigns to stop it. Qat production has, in turn, become part of the economic mainstream, producing up to five times the payoff of other crops. The cycle has been tough to break.

With so few other national bonds, Yemen has more to pull it apart than to hold it together. Six weeks after our trip, the first civil war since unification erupted between the country’s two former halves—the republican North Yemen and the socialist South Yemen. The south revolted against the autocratic cronyism of President Ali Abdullah Saleh, the former leader of North Yemen, who had assumed over-all control after the merger. The southerners lost, several leaders fled into exile, and Yemen has been riven by conflicts ever since.

The current Houthi rebellion—the seventh—is only the latest. The Houthi clan are Zaydi Muslims, who make up about a third of Yemen’s twenty-six million people. A once powerful people from the rugged northern highlands, they ruled an imamate for a millennium and deeply resented their reduced influence under Saleh. Between 2004 and 2010, they fought six other wars against his government.

Meanwhile, the long-simmering separatist movement in the south picked up steam again, in 2009. It has played out in sporadic armed attacks, general strikes, and peaceful protests. The main flashpoint—the failure to share power since unification—was the same that triggered Yemen’s 1994 civil war. Southerners also resented the hoarding of national revenues by Sanaa, the former capital of North Yemen that became the unified capital.

The internal turmoil left uncontrolled pockets of territory filled by Al Qaeda, especially after Saudi Arabia’s crackdown forced extremists to flee across the border in 2004. U.S. drone strikes have killed Al Qaeda operatives but haven’t stopped operations, in Yemen or abroad. By 2010, the C.I.A. ranked the reconfigured Al Qaeda in the Arabian Peninsula, based in Yemen, as the most dangerous threat to U.S. security.

Saleh’s ruthless rule was unable to hold Yemen together. In 2011, a national uprising—inspired by the Arab Spring—ousted Saleh after almost a quarter century in power. The state only grew frailer. The six Gulf sheikhdoms, led by Saudi Arabia, orchestrated a transition. But the subsequent National Dialogue among the nation’s notables, tribal leaders, and even a Nobel Peace Prize winner—the Yemeni blogger and politician Tawakkol Karman—failed to cobble together either a constitution or a power-sharing formula. The unravelling of one of the world’s most exotic countries accelerated.

Last September, the Houthis—who have picked up support beyond their own power base during the cycles of conflict—seized Sanaa. In March, a ten-nation coalition, again led by the Saudis, launched military strikes to stop the Houthis, who have allies in Iran (they are from different branches of Shiite Islam). Yemen is now a regional conflict, too.

The quarter-century experiment in uniting Yemen has definitively failed. There is no military solution, and there are unlikely to be any winners out of such a multilayered conflict, whatever the territorial gains.

On Tuesday, the International Committee of the Red Cross spokeswoman Marie Claire Feghali warned that Yemen had also become “a catastrophe, a humanitarian catastrophe.” Food, fuel, water, and medicine are now in short supply, aid agencies are warning. “It was difficult enough before, but now there are just no words for how bad it’s gotten,” Feghali said. At a press conference in Riyadh, Yemen’s Human Rights Minister, Izzedine al-Asbahi, said that the fighting had taken Yemen, already one of the world’s poorest countries, back at least a century.