Clouds of uncertainty and foreboding hang over Kabul as heavily as the traffic pollution, which obscures its once stunning vista of surrounding mountains. Eleven years after the west's military intervention, the withdrawal of US, British and other international forces has started, but no one knows whether their departure will lead to more or less instability for a country that has been mired in civil war for almost 40 years.

Most Afghans say they are happy to see foreign troops depart, yet many are also concerned at the vacuum they will leave, in spite of international pledges of billions of dollars for the next decade. In seven visits to the country since the Taliban were toppled I have never found the Afghan mood so febrile and gloomy.

Disappointment and bitterness are widespread. Long gone are the high hopes sparked by regime change in 2001. The foreigners delivered far less than they promised. Kabul was transformed into a canyon of concrete blast walls and watchtowers shielding enclaves from which foreign diplomats only emerge in armoured vehicles for official contacts. Journalists, NGO staff and independent westerners who have lived here for years sense a rising mood of anger, and most have stopped going around Kabul on foot for fear of hostile looks, insults hissed in Dari or Pashto, or stones being thrown.

While Afghans blame government officials for creaming off much of the aid money, they blame western donors for doing too little to reduce corruption. US military commanders who handed out cash for "quick impact" projects are accused of encouraging it.

Most diplomats still peddle cautious optimism about "progress, albeit fragile", as the US and UK hand military responsibility to hastily trained Afghan National Security Forces (ANSF). Few Afghans share it. The new rich are getting their money or their families out to Dubai and other Gulf states. Many are putting their houses on the market so as to acquire the cash to leave. Used car agents report more sellers than buyers.

While the official narrative speaks of the ANSF increasingly taking the lead on the battlefield, it is obvious they are inferior in experience and equipment. In many instances US commanders no longer provide close air support or medevac facilities to embattled Afghan units – a dramatic sign that Afghans are on their own. One theory for the recent rise in "green-on-blue" attacks by Afghan troops on their western allies is that it flows directly from the rise in joint operations. Working closely with western troops gives Afghans direct experience of the difference in facilities and "culture". They resent the brutality of raids on family compounds in which they are asked to take part.

The withdrawal of US troops has already meant a loss of territory. In provinces where the US has closed forward operating bases, the Taliban and the other main insurgent group, Hezb-i Islami, have moved in to fill the gap. The trend is likely to grow throughout 2013 as the Afghan countryside becomes a much larger patchwork of areas contested between Taliban and government forces than it is today. Few think Kabul will fall in a hurry, but the Taliban will take hold of hundreds of district centres in the Pashtun south and east. Traffic on the main roads will face an array of checkpoints, some controlled by the ANSF, some by the Taliban, and some by local warlords or armed criminal gangs. For ordinary Afghans there will be a perceptible decline in security.

Ten years of relentless anti-Taliban propaganda, the relative safety of Kabul and infusions of money for school and university expansion have produced a new generation in the capital city who sound optimistic. But some young people are leaving. A broadcast journalist said her son was upset because his friends' families were saving up to pay people-smugglers to get them to Europe. He felt isolated and depressed at not going too. In NGO offices around Kabul, activists in their 20s and 30s are still spending donors' money on a host of projects from women's empowerment to mental health centres and the development of independent media. They know their funds will soon be cut.

A massive surge in unemployment is approaching. The vast army of translators, drivers, cooks and bottle-washers who serve the occupation forces will shrink throughout next year. The provincial reconstruction teams – the bases where foreign advisers and consultants sit and monitor aid delivery – will close. The result will be a dramatic curtailment of projects, since foreigners will no longer be able to supervise them.

Optimists in the Afghan elite believe there is still a chance to win popular support for the government in the two years remaining before foreign troops leave. They want to ensure that the presidential and provincial elections, due in 2014, are clean this time. This would weaken the Taliban claim to provide justice more effectively than the predators and brigands who now dominate local and central government. But many doubt that much improvement can be made in a single year when a decade has produced so little.

Outside Afghanistan, public interest has collapsed. In Europe and the US, people want out, and care little whether the whole adventure is seen as a defeat. It was remarkable how minor a role the war played in the US election. There will be less demand for a grand reckoning of policymakers' blunders than there was for Iraq.

The American and British people were largely complicit, since the revenge attack on Afghanistan after 9/11 had widespread approval, and certainly more than the invasion of Iraq. In Kabul there was a greater welcome for the foreign occupiers than in Baghdad or Basra. The Taliban had less of a support base than Saddam Hussein. But with their failure to anticipate that western armies cannot remain popular for long when they invade Muslim countries, Bush and Blair are guilty of as great a folly as they were in Iraq.