Nobody will admit this, obviously. For most of us the truth is too hard to bear. It requires accepting just how pointless the loss of 41 Australian lives was, along with the more than 454 British, 2,298 Americans and hundreds of thousands of Afghans who've also died as a direct result of this conflict, 120,000 of them wearing uniform.

That's quite apart from the billions and billions of dollars that have vanished, the flourishing drug production, and the millions now displaced without home or hope.

But make no mistake. Washington has now decided that this ending, terrible though it is, is far better than continuing to leave open the tap that's dripping lives and money into an endless, insoluble, ocean of conflict and despair.

It's been a long time coming but finally all the pieces have clicked into place. You will never hear anyone admit it (at least for a couple of years) but although this is not the way anyone ever wanted things to end - the reality is that this outcome became inevitable the moment that Kabul refused to make a deal with the Taliban.

In Washington, however, invisible glasses of champagne will soon be raised in quiet toasts.

The West is out of Afghanistan! Finally!

The ultimate decision-maker was Joe Biden. Remember that he began engaging in the intricate detail of attempting to solve this puzzle when serving as Veep under Barack Obama. He's met the players and understands the one, critical fact that eventually led to America's decision to withdraw support to the Kabul regime: it is insolubly incompetent.

The cause of this dates back to Washington's original decision to support the leader from central casting, Hamid Karzai, to chair the country's interim administration in December 2001.

Back then with no country to administer and nave graduates wearing Brooks Brothers slacks and talking about fertile fields of democracy blooming in the heart of the Middle East, everything seemed possible.

Karzai was anointed saviour and, even though he could never win an un-rigged election and although this imposed an inappropriate, Western model of governance on a divided, medieval country where consensus from collaborative councils (or shura) would have been more appropriate, America announced the Afghan question had finally been solved. The superpower then departed to invade Iraq.

Enter Barack Obama, pontificating about "the good war". He was so certain he could find a solution, but hope turned out to be just a slogan.

Obama ignored successive options aimed at easing the US out of the deepening quagmire and deployed more troops. Perhaps this would allow governance to become better?

Alas, more money simply led to more corruption and more foreign soldiers bred more resentment.

Maybe backing a few warlords would permit the eventual development of a thriving economy?

No, alas, the easy rewards of opium production wrecked other crops and corruption flourished. Could a pin-point bombing campaign eliminate the Taliban's leaders and provide success where soldiers couldn't? No. It simply alienated more civilians while killing off any chance of negotiations.

Obama was full of wonderful rhetoric but utterly incapable of turning it into practical solutions.

In 2014, after another rigged and eventually ignored election Ashraf Ghani became president in Kabul. In the countryside, the killing continued.

Then came four years of dysfunction. Donald Trump oscillated, supporting the generals (who wanted, of course, more war) while opening negotiations with the Taliban (who wanted power). And still the killing went on.

When Biden entered the Oval Office, this time as decision-maker, his resolved not to intervene but allow events to play out.

It will take time before we properly understand the detail, however the fact that he is limiting the deployment of troops in to ensuring an orderly withdrawal speaks volumes.

If Biden wanted to prop Ghani up he could, easily. It wouldn't take much more than deploying a brigade, coupled with extensive and intimate air support, to halt the cascading collapse of Afghan forces.

The US is already committing nearly that many troops simply to extract civilians.

But he won't, as the decision to pull out our own diplomats reveals. Scott Morrison knew there was no stomach in Washington to support Ghani and that's (partly) why he overruled Marise Payne's objections and ordered our diplomats out.

The fix has been in for some time, it just hasn't been communicated to the wider public.

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The players in Afghanistan know what's going on, however. That's why the Tajik and Uzbeks who used to form the backbone of resistance to the Taliban, the old Northern Alliance, have now switched sides. It's why Orzgan governor Omar Sherzad, who once promised to crush any assault on Tarin Khot, has now thrown in his lot with the insurgency. It may still be a while before this offensive culminates in the installation of a new government, but its result is not in doubt.

The scenes about to occur in Kabul are just the final, inevitable, culmination of a two-decade process of unwinding the failed model of government chosen for the country back in the months after the 2001 invasion. This result became inevitable as soon as the White House withdrew its support. Did Ghani not realise this, or did he just think Biden was bluffing? Whatever. Welcome to the world of realpolitik.

This should only come as a surprise to people who believed in the hope proffered by politicians like Obama and Kevin Rudd, or perhaps others who had an inflated idea of our ability to change a deeply ingrained foreign and ancient culture.

It turned out their promises were empty. Just hoping our deployment would bring peace and development to Afghanistan was never going to be enough. Accomplishment requires much more than just hopes and good intentions. But who could have guessed all that effort and work could collapse so very fast?