As the final evacuation flights leave Kabul, watched in despair by those abandoned and in peril, the lasting consequences of strategic failure must now be faced. During the Doha peace talks, American diplomats liked to talk of a process towards an inclusive political settlement that would be Afghan-led and Afghan-owned. The “process” turned out instead to be a victory procession for the Taliban. What comes now will therefore be Taliban-led and Taliban-owned. Hamstrung as a result of their own mistakes, the United States, Britain and their allies have little choice but to engage with the new reality.

Belated attempts are being made to do so from a supposed position of strength. As the last British forces left Kabul at the weekend, Boris Johnson adopted a stentorian tone to warn: “If the new regime … wants diplomatic recognition or to unlock the billions currently frozen, they will have to ensure safe passage for those who wish to leave the country, to respect the rights of women and girls, [and] to prevent Afghanistan becoming again an incubator for global terror.” It seems clear that Taliban leaders hope to avoid the international pariah status of the 1990s and will soon be in desperate need of cash. Both the International Monetary Fund and the World Bank have suspended payments to Afghanistan since the Taliban takeover, and the Afghan central bank’s reserves are frozen in the US. But the notion that, as China and Russia pursue their own agendas, the west can continue to call the shots and impose its terms is wishful thinking.

Unfolding humanitarian crises will limit the scope for playing diplomatic hardball. Over the weekend it emerged that, despite the huge evacuation effort from Kabul airport, British government estimates of the number of vulnerable people left behind were far too low. There is no plan in place for what those left stranded should do now, and no route established yet for refugees to neighbouring countries. Demonstrating extraordinary negligence, the foreign secretary, Dominic Raab, failed even to engage with his Pakistani counterpart until a week after the fall of Kabul to the Taliban. On Monday, the German foreign minister, Heiko Maas, began a diplomatic tour of countries bordering Afghanistan, including Pakistan, in the hope of securing refugee agreements which should have been negotiated months ago.

According to a joint statement by the UK, the US and more than 90 other countries, the Taliban have given assurances that foreign nationals and Afghans with travel authorisation from other countries will be allowed to leave. This seems at odds with reports of house-to-house searches and the intimidation of those associated with the former government and western forces. But in the absence of any leverage in the country, America and its allies must simply hope that the Taliban’s calculation of their self-interest works in the west’s favour. Meanwhile, soaring food prices, prolonged drought in much of the country and the internal displacement of millions of refugees – many of them women and children – are already leading to appalling hardship as autumn and winter approach. It will be impossible to deliver to desperate Afghans the scale of humanitarian assistance required without some degree of cooperation and collaboration with the new regime.

On Monday, the Kremlin called for Washington to release the Afghan central bank reserves on humanitarian grounds, while in a phone conversation with the US secretary of state, Anthony Blinken, the Chinese foreign minister, Wang Yi, said that the international community should engage with the Taliban and “guide it actively”. By failing to link military withdrawal to conditions on the ground, the west no longer controls the course of events. In relation to the Taliban regime it inadvertently installed, it has no good options now.