America's longest war, it ended faster and more chaotically than anyone had ever anticipated. From the moment US President Joe Biden announced in April that all US troops would be gone from Afghanistan by the end of August, there were warnings about the message it would send to a potentially resurgent Taliban.
The US had led the invasion of the country two decades before meaning its departure would also see all remaining allied forces leave too, including the UK which had stood shoulder to shoulder with the US in the early days of the war.
In the end even those who warned that the US withdrawal might see the Taliban take advantage of a political vacuum were astounded by the speed with which that vacuum filled.
In a few short weeks Afghanistan's past became its present and its future as the Taliban, once again, took control across the country, entering Kabul on 15 August as international troops and citizens scrambled to leave the country as fast as possible.
During the evacuation, so-called Islamic State launched a suicide bomb attack on the crowded gates of Kabul airport, killing scores of civilians and 13 US troops, the deadliest incident for US forces in Afghanistan in more than a decade.
The rapidity of the US departure left many Afghans who had a right to travel stranded where they were. Many remain, hoping they can still get out. Some are in hiding from a Taliban which wants vengeance for what it perceives to be their disloyalty. Some will never reach safety, having been killed by the Taliban in the months since they took power.
In the days after its takeover, the Taliban talked of how it would rule differently now to how it had done in the past. Assurances that there wouldn’t be a return to the harsh fundamentalist view of 20 years before were greeted with scepticism by the international community.
That scepticism deepened as the Taliban excluded representatives of other sectors of society and curtailed the rights of women and girls, which included stopping them from going to school and work.
In recent weeks the United Nations Deputy Commissioner for Human Rights Nada al-Nashif said the UN believes that more than 100 former Afghan national security forces and others have been killed since the Taliban takeover in August, mostly at the hands of the Taliban.
In a speech to the Human Rights Council in early December, she described Taliban rule as being marked by extrajudicial killings across the country and restrictions on women's and girls' basic rights.
At least 72 of the more than 100 alleged killings have been attributed to the Taliban, Ms al-Nashif said, adding: "In several cases, the bodies were publicly displayed. This has exacerbated fear among this sizeable category of the population."
It is against this backdrop of extrajudicial killings and human rights abuses that the international community is struggling to find a way to work with the Taliban, as it faces a mounting humanitarian crisis.
Earlier this year, as one province after another fell under Taliban control, aid agencies warned that the new regime would have to be acknowledge and accommodated, however distasteful many would find it. In the months since western forces left that need to find common ground has only become more urgent.
The abrupt withdrawal of foreign aid following the Taliban victory has pushed Afghanistan's fragile economy close to collapse. An ongoing drought has exacerbated the situation. Millions are without work and the banking system is only partially functional. Surging prices mean that even those who could once afford food now can’t.
The statistics relating to Afghanistan are calamitous. Almost the entire country - 97% of people - are thought to be without enough food with the World Food Programme describing the situation as "an avalanche of hunger and destitution".
A million children face imminent starvation according to UNICEF with ten million children at risk form extreme food insecurity. The arrival of the first snows in Kabul this month stand as a reminder of the harshness of the Afghan winter, made all the more harsh for a people without enough food or heat.
With the Taliban struggling to convert a lightning military victory into an ability to govern, the reaction of the international community is crucial if a large scale humanitarian disaster is to be eased to any degree.
2021 was a tumultuous, volatile and often desperate year for Afghanistan. 2022 looks as if it will be little better.