For all that it had been warned of, was perhaps even half-expected, Thursday’s terrorist attack on Kabul’s Hamid Karzai airport was a deeply shocking event. The setting for the final unravelling of the west’s failure was already frightening. Thousands of people had struggled for days to gain access to the buildings and officials that they hoped would offer them a passport to safety. With Islamic State’s attack, which began not far from the Baron Hotel where British personnel were based, and is so far known to have killed 79 civilians and 13 US service people, what had been a worst-case scenario became reality.

Islamic State’s Afghan affiliate, known as Islamic State Khorasan Province and also as Isis-K, detonated a bomb that not only ripped apart lives, but also served as a bloodcurdling warning of what it may be capable of. Joe Biden, unsurprisingly, responded with a threat of his own: “We will not forgive. We will not forget. We will hunt you down and make you pay,” he said, following the carnage, addressing the terrorists directly for the benefit of an appalled domestic audience.

What happens now is that the evacuation continues amid hugely elevated distress. Mr Biden has refused to waver from next Tuesday’s deadline, with the UK effort due to conclude before the weekend. On Friday, it was clear that even bombs had failed to deter the crowds bent on escape. Queues continued to form at the sewage canal close to the airport, while administrators failed to keep pace with demand for documents to be checked. Ben Wallace, the UK’s defence secretary, acknowledged that some of those entitled to come to Britain because they had worked for the embassy or military would be left behind. Others pointed out that his figure of 1,100 was an underestimate.

The longer-term impact of the attack is harder to assess, beyond the obvious point that it is alarming – or terrifying, if you are an Afghan – that an Islamic State offshoot now occupies the position that it does. Much will depend on the capacity of the Taliban to withstand this assault on their authority, and on developing relations between the various strands and strongholds of extreme Islamism both within and beyond Afghanistan’s borders. Much faster than the west expected, the Taliban filled the vacuum created by the withdrawal negotiated by Donald Trump and enacted by his successor. Now, before the Americans have even left, the Taliban themselves are being confronted.

The danger is that the Afghan state and civil society, after the west’s shamefully conducted withdrawal, will collapse altogether. Already, 300,000 people have been displaced following the Taliban’s advance over the summer. Three-quarters of all public expenditure (on hospitals, schools and so on) is derived from foreign aid. There is no reason to have any confidence in the Taliban’s governance capabilities. But things are likely to be even worse for Afghanistan’s population of almost 40 million, above all the women and girls who are already having basic rights such as education removed, if their leaders become consumed by factional infighting and paranoia. Already, following the attack, there are reports of unprecedented numbers of Afghans feeling across the border to Pakistan.

Western countries, including the UK, must honour their obligations, not only to those who worked for them, including the refugees who must now be found homes and jobs, but to Afghan society as a whole. The international community should find common cause in the attempt to give the people of this broken country a chance. From a western perspective, this week’s explosion may have the appearance of a parting shot. For Afghans, the fear is that it marks the start of yet another bloody chapter.