Pictures of helicopters extracting embassy officials from rooftops are carbon copies of those we saw of the fall of Saigon. To use a pop-culture reference as a purely strategic analogy, the defeat of Western military forces in Afghanistan is akin to the destruction of the UFOs in the movie Independence Day.

Yet events did not need to transpire like this. The war in Afghanistan was 100 per cent winnable had sage strategy prevailed. Moreover, unlike in Vietnam, the vast majority of Afghans wanted us to win - badly.

The North Vietnamese took their tactics from the Imperial Japanese Army, and were influenced heavily by what turned into the guerilla defence of those portions of the Pacific the Japanese captured during World War II. The Taliban, however, were trained in the art of the flea by none other than the CIA, whose remit in Afghanistan and Pakistan during the Soviet invasion did not include concerning themselves with what the world would look like after the Soviet Union was defeated.

And so Afghanistan has come full circle, the big players having been played. Never in the history of insurgencies has a king been checked by a pawn so thoroughly, or so consequentially. From day one the Taliban played the long game, a game impetuous Western militaries had no real interest in playing. Australian, British and American forces alike played checkers over chess, thumping their own chests after every tactical success against an enemy who knew winning meant abandoning the tactical field and concentrating on setting the strategic conditions for success.

Foreign sanctuaries, a classic and patient policy of death by a thousand cuts on the battlefield, penetrating security services to break the trust between trainer and trainee - to the extent that the Afghan National Army's training was subordinated to the security of the trainers - all formed an undefeatable situation militarily.

Early on there was coalition hope, fuelled by the assumption that the British military - given their experiences in Malaya, Oman and Northern Ireland, campaigns considered the halcyon of counter-insurgency practice in most textbooks - would influence and guide the effort away from Saigon redux. However the British bulldog did little more than chase its own tail in Helmand province like everyone else (with the notable exception of the Dutch, who were the strategic stars of the war).

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Very early on the Americans deliberately decided to prosecute a counter-terrorism campaign (Vietnam-era military lingo for search and destroy) in lieu of counter-insurgency. And so the Australians and British dutifully followed them off the cliff. They failed to appreciate just how well CIA field officers had trained the mujahideen. Everything flows from that seminal campaign, and we see now how the master has become the apprentice. Over the last few weeks the Taliban's masterclass in insurgency has come in the form of one exceedingly simple but strategically profound battle plan - assassinating Afghan military pilots.

Without air support, the ANA has been unable to stop the flow of Taliban fighters who have, after 20 years, shifted to offence so fast even Western intelligence agencies were stunned (assuredly for having based their assessments on proffered military assessments for two decades). With residual Western air support, the Afghans could have held off the Taliban for, frankly, as long as it took. Even simply postponing the withdrawal of Western troops until the winter (campaign off-season for the Taliban) could have made all the difference and allowed Kabul to coalesce its forces to block the border points where Taliban technicals (gun trucks) have poured in from Pakistan - maybe. But for some reason, long-standing Western counter-insurgency praxis seems to turn at a particular point to petulantly wiping the chess board.

The loss of military deterrence due to this latest in a rolling string of generational military defeats cannot be understated. The September 11 attacks demonstrated that, unlike Vietnam, the security implications of losing this war are not theoretical. The only saving grace may be that, given the response to those attacks, the Taliban may not permit another attack on Westen soil. However, that is now, like the discredited domino theory, a purely academic argument (until it's not).

The one indisputable fact to flow from the Afghan war is that Western militaries can now be essentially classified as combat-ineffective. That's something that will inevitably change the threat assessments made by Chinese and Russian planners.