The head of the British military has admitted that western forces did not have “insight and understanding” of Afghanistan before invading the country.
Gen Sir Nick Carter also suggested the army had not been defeated by the Taliban but had been let down by poor political judgment.
During an at times heated appearance before the House of Commons' defence committee, he argued that the current Taliban regime were more moderate than the extremists who controlled Afghanistan between 1996 and 2001.
The UK Chief of the Defence Staff was questioned for two hours by MPs over why the “mightiest forces ever put together” with the superior military technology of the US and UK were unable to overcome an enemy armed with AK47s and rocket-propelled grenades.
“None of us had adequate insight and understanding of the nature of the challenge in Afghanistan before we got involved in it,” Gen Carter said.
He described the Taliban as “very cunning, ruthless and innovative”.
He said that when the West looked at the lessons from Afghanistan it would need to understand “the political dynamics of the use of the military instrument”, suggesting it was the politicians who misused the military.
Gen Carter, 62, also insisted the western armies had not been defeated. “It was the politics of it that were very challenging to resolve," he said.
When the Nato operation began in earnest in 2005, many Afghans fought for the Taliban in the belief their country had been invaded by foreigners. Some were killed, which ultimately sustained the insurgency, he said.
“A number of people were killed and probably their families became the enemy and that whole thing became a very difficult political challenge to resolve,” he said.
“So, it doesn't matter how effective one’s military machinery is, if it's not being used in the right way, in terms of the politics of the region and the country that you're doing this, you will fail.”
But he suggested western forces could return to Afghanistan, either through an unsustainable Taliban government or a resurgence by ISIS-K, an affiliate of ISIS.
“It depends how well the Taliban do in governing the place and that's going to be quite a challenge,” he said.
“We already know about the humanitarian crisis that's very worrying. We already know that ISIS-K is becoming more of a thing.”
But there was as yet no “true indications that international terrorism is alive and well” in Afghanistan, suggesting that Al Qaeda not yet been revived.
He also admitted it would be difficult to conduct counter-terrorism strikes without a military presence in Afghanistan.
Gen Carter, who leaves his post next month after 45 years of service, suggested the current Taliban were more moderate than their predecessors.
“Taliban 2.0 is different. There are a lot of people in Taliban 2.0 who would like to govern in a more modern way, but they are divided among themselves, as political entities so often are,” he said.
If the “less repressive elements end up gaining control” then it is possible that Afghanistan can have a more inclusive government, he said.
Asked whether there should be a public inquiry into what went wrong in Afghanistan, Gen Carter said: “I think there are lots of lessons that we can learn from this."