The crisis in Afghanistan is a “pretty fundamental moment” for the special relationship between Britain and the United States, according to British officials.

The UK privately complained after Washington chose not to consult London earlier this year before US President Joe Biden made his decision to pull out the majority of his forces from the country, forcing Britain to do the same and setting in train a Taliban takeover.

Critical voices in Britain have since become more public as frustration grows at the chaotic fallout from the US-led exit, symbolised by the catastrophe outside Kabul airport as Afghans desperate to flee Taliban-rule risk their lives trying to board evacuation flights.

But Biden‘s unilateral action on Afghanistan was the product of a reality the UK and other NATO allies have created – where the US was the predominant military power on the ground and the ability of others to influence was increasingly limited.

The Afghan intervention has also exposed another more fundamental limitation – that of the political will of the US, British and other western governments to withstand the pressures of a complex and costly campaign in a distant country that poses no immediate threat to them.

Once emotions calm, instead of embarking on a blame game, allies should unite to learn collectively the lessons from what went wrong.

If they do not then their retreat – which already has disastrous consequences for Afghanistan – could inflict lasting damage on the balance of power between the world’s democracies and authoritarian regimes.

Over the weekend, Tony Blair, the former British prime minister, framed Afghanistan as a strategic failure for Western powers – raising the spectre of Biden leading the world’s democracies into “epoch-changing retreat”.

But this failure of grand strategy by the West began on his watch and was compounded by successive political, military and diplomatic leaders.

On this point, Blair simply wrote: “We made mistakes, some serious”.

They weren’t just serious. The mistakes of the past set the stage for today’s failures.

Experts cite the gravest among them being a US-led decision, supported by Blair, to invade Iraq in March 2003 on the futile hunt for weapons of mass destruction.

The move diverted political, diplomatic and military attention as well as resources towards Baghdad and away from Kabul, where the Taliban had been swiftly toppled and the terrorist training camps of al Qaeda severely disrupted.

In an article published on his website, the former prime minister is rightly critical about how “intervention requires commitment. Not time limited by political timetables but by obedience to goals”.

Yet once committed to the politically unpopular war in Iraq, he did not heed his own advice, instead choosing to start drawing down troops in the south of the country too soon.

It meant UK ambitions to build up the Iraqi security forces and hand over control to the Iraqi government in the southern city of Basra floundered in the face of an Iranian-backed militia.

Ultimately, the US had to step in to help Iraqi troops regain control of the south in a humiliation for the UK – though one that the special relationship was able to endure, as it doubtless will again despite the repercussions from Afghanistan.

Blair was also still prime minister when in 2006, while committed to the war in Iraq, the UK switched focus and resources yet again back to Afghanistan to deploy to the south.

The Helmand deployment was a debacle from the start, with one former military commander saying Britain’s leaders deployed troops with “their eyes shut and fingers crossed”.

Washington again had to step in to support the over-stretched British effort. But when then President Barack Obama agreed in 2009 to surge US forces into Helmand in large numbers, it ultimately came with a calendar-based rather than a conditions-based timetable for withdrawal from Afghanistan.

The UK and other NATO allies followed suit, setting the clock ticking for the events of today.

Finally, when considering UK-US relations and western failure in Afghanistan, it is worth remembering – with the exception of special forces – Britain’s combat mission in the country ended in 2014 and most troops left.

The US had wanted the UK to commit more service personnel to an enduring NATO training mission but then prime minister David Cameron declined. It meant Britain even lost its place as the second-largest troop contributor to Germany.

Many other NATO allies also failed to commit the number of troops recommended for the mission, leaving the US once again to do most of the heavy lifting.

It was a status quo gifted to Donald Trump when he took over from Obama.

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He ultimately chose to cut a deal with the Taliban – again a move the UK and others were largely sidelined from – agreeing that all US forces would withdraw by May 2021.

Biden, with a history of scepticism on the enduring effort in Afghanistan, inherited the Trump deal. He decided, rather than overturn it and risk more US casualties in a renewed fight with the Taliban, he would extend the exit date by a few months but still leave.

Had Britain and other NATO allies been more meaningfully included in the deliberations might the outcome have been different?

If they had been willing throughout the past 20 years to take on the political, military and financial risk of committing to the mission in greater numbers and not on a calendar basis then it is hard to see how it would not.