In 2001, U.S.-led NATO forces invaded Afghanistan to hunt down Al Qaeda and take down the Taliban government. In the years that followed, fifty-four billion dollars came into the country in the form of economic aid and military spending. War-related industries sprouted and prospered: construction, logistics, and security. The country’s official per-capita G.D.P. more than quadrupled from 2001 to 2010. There was rampant corruption and graft, but the country also saw concrete improvements: The maternal mortality rate dropped by half from 2000 to 2011, and life expectancy rose by nearly four years over that period.

This year, Afghanistan’s G.D.P. is expected to grow 3.7 per cent, down from growth of twelve per cent in 2012, according to a projection by the World Bank. In Kabul, drug addicts can be seen squabbling over heroin at traffic islands in broad daylight, and day laborers mill around on street corners, desperate for low-paying work. “The thing about a bubble is that it bursts,” Kate Clark, a senior analyst with the Afghanistan Analysts Network, said. “Some things you don’t lose, like education or aspiration,” Clark said. But she wonders what will happen to the young men and women who have reaped the benefits of the past decade and gotten used to comfortable lives replete with education and employment opportunities. “Particularly when you have so many young men out in the job market like we have now, I think there is going to be trouble ahead,” she told me.

When I was house-hunting in Kabul earlier this year, most of the available properties were the abandoned facilities of long-departed international organizations. They were compounds with servants’ quarters and gussied-up gardens, houses meant for a different era, when it seemed like the wartime wealth would carry on forever.

In the chill of a mid-March morning, I climbed inside one of Kabul’s many vacant structures to meet some members of the middle class. The bare scaffolding of a construction site was serving as an informal shelter for men who had traveled from the provinces in search of jobs. Many were university-educated professionals who had Facebook accounts and listened to the BBC.

One of the men—who had been sleeping on a thin mattress on the concrete floor—had previously administered a U.S.A.I.D. program in the south. Abdul Manan, twenty-seven years old at the time of our conversation, seemed despondent—not only about losing a good job, but about what would happen when American money stopped flowing to the rural districts where he had run agricultural projects, supplying seeds to farmers. “We all knew that this new wealth wouldn’t last forever, but what we didn’t understand was how quickly it would evaporate,” he said. “We were all hoping that it would last for some time. This is a mistake I made.”

The full economic impact of the troop withdrawals is difficult to measure, as it depends on factors that are hard to predict, such as whether the Taliban rises again. The last time that the U.S. stopped paying attention to Afghanistan, after the withdrawal of Soviet troops in the late nineteen-eighties, civil war ensued.

Some worry that Afghanistan is now primed for similar troubles. In 2010 and 2011, annual foreign aid of nearly sixteen billion dollars comprised ninety-seven per cent of the country’s G.D.P., according to the World Bank. The Afghan government has warned that without continued foreign assistance, the country will collapse, undoing twelve years of counterinsurgency efforts led by the U.S. The World Bank warns that an abrupt cutoff in aid could lead to a collapse of political authority, promote the illicit drug market, and incite armed conflict.

The United Nations Office on Drugs and Crime found in a 2013 report that opium cultivation had increased in the past three years. If that pattern continues, the report said, opium will become Afghanistan’s leading source of income. The highs of opium production coincided with NATO engagement, but Jean-Luc Lemahieu, the head of the U.N.O.D.C.’s office in Afghanistan, believes that the worst might be ahead. “Money is drying up, so you don’t have the same access to private security, transportation, or construction contracts. All that is on the decline. But there is still the demand for money, so you see the illicit economy—opium production being the main one—kicking in.”

Others are more optimistic. Karim Khoja is the C.E.O. of Roshan, the country’s largest telecom provider. He has seen at least five men in his business community kidnapped in the last five months, he told me, but thinks that the past decade of progress will help temper religious extremism. “Ten years ago, when I first came to Afghanistan, there was no Facebook or Twitter,” he said. “Now, when you drive around Kabul, there are wedding halls, traffic on streets, storefronts with customers. We have football games. These are things you would have never heard of a decade ago.”

The U.S. Geological Survey has identified a trillion dollars’ worth of mineral resources, which could help soften the impact of any recession. But the development of that sector would require regulation and infrastructure. It will not be easy to construct what’s needed for a modern mining industry—railroads, for example—in remote parts of the country where government control remains tenuous. There remains, too, the threat of corruption.

In August, I caught up with the men I’d previously met at the men’s shelter. Over tea at my house, one of them, Siraj Agha, told me that after being unemployed for six months, he had taken a job as a bookkeeper at Kabul’s Sarai Shahzada currency market. The work paid four hundred dollars a month, a dramatic cut from the eighteen hundred dollars a month he once made at a U.S.A.I.D.-funded project. Agha explained that, on a tight budget, he could no longer afford to entertain. “These days, I don’t see my friends much,” he said.

He was sending half of his salary to his family in the south. At thirty-five years old, Agha remained a bachelor. He wanted to get married, but weddings in Afghanistan are tremendously expensive affairs, and Agha said he cannot afford such luxuries.

Abdul Manan had also found work. He complained that he was doing the same thing he was doing before, organizing peace shuras—consensus-building assemblies—but getting paid thirty per cent less. Manan was most troubled that he has had to scale back his ambitions for his children. “I was planning to educate my children in the best schools, but I have to rethink that,” he said. “There are many things that I want for them that I cannot afford anymore.” All the spending by international groups has also led to inflation, he pointed out, which has driven up the costs of all kinds of products and services. “A burger that should cost fifty Afghanis now costs two hundred,” he said. “A haircut that was one dollar before is now ten dollars.”

Indeed, a 2013 World Food Programme study found that this year’s daily wage for an unskilled laborer in Afghanistan would purchase thirty-five per cent less wheat flour than in the same period last year. “Per capita G.D.P. has gone up, which looks good on paper,” Clark, the analyst, told me. “But at the same time, the cost of living has also gone up.”

Photograph by Farshad Usyan/AFP/Getty.