Twenty years of war, after the 9/11 attacks hatched by al-Qaeda in Afghanistan, have killed an estimated 241,000 people there. America has spent billions building a state and security system now collapsing like a pack of cards.
Taliban fighters have taken 18 of Afghanistan's 34 provinces with ineffective resistance from the rebuilt Afghan army, amid mass surrenders.
It has been very reminiscent of when Isis crushed the similarly Western-fashioned Iraqi army in 2014.
The advance in the void has been so rapid that the US, Britain and Canada have had to send troops back to ensure the airlift evacuation of their diplomats and some Afghan people from Kabul - a Saigon 1975 moment as the Taliban enter the capital's outskirts.
Afghanistan, and the other "war on terror" conflicts, have drifted on for years in a lower-level stalemate. Together, military action in Afghanistan, Pakistan, Iraq and Syria have cost the US more than US$6.4 trillion over 20 years.
One estimate this year, which included wider US costs, put the amount for Afghanistan at US$2t.
These estimates look particularly bad in 2021 with the world in the thick of the climate crisis. Imagine if those trillions had been spent instead on reducing carbon emissions over the past two decades.
America's decision to give up and get out began under the Trump Administration and was followed through by the Biden Administration. A YouGov poll in April showed majority support for the move.
US President Joe Biden last year told CBS when asked about Afghanistan that America shouldn't "try to solve every single problem in the world by use of force". He's now had to order 5000 troops back for the drawdown.
The messy end doesn't sit well with foreign policy experts. Richard Haass, the president of the Council on Foreign Relations, tweeted: "The US & its allies had reached something of an equilibrium at a low sustainable cost. It wasn't peace or military victory, but it was infinitely preferable to the strategic & human catastrophe that is unfolding."
The Taliban's power grab has stirred fears for Afghanistan's people generally and particularly for those who have worked with the foreign troops.
There could be fighting between factions, there's already major displacement of citizens. It's the end of what many hoped would be a better place. Taliban rule is likely to be a huge setback in people's lives, especially for women and girls.
About 5000 locals who worked with the US are being located but tens of thousands are seeking refuge. Canada has proposed taking in 20,000 refugees from Afghanistan.
The main lessons here are sadly familiar ones: the expensive follies of interventions without clear endgames; the limitations of outsiders attempting to rebuild states and armies; and the pitfalls for locals of relying on foreign protectors.