The former head of the coalition forces in Afghanistan, General Stanley McChrystal, says after 10 years there, the United States still lacks the knowledge to bring the conflict to a successful end.
Speaking at the Council on Foreign Relations, General McChrystal, who commanded coalition forces in 2009-10 before being forced to resign after a magazine interview, said the US and Nato allies were "a little better than" half way to achieving their military goals.
He told the Council the US began the war with a "frighteningly simplistic" view and still lacked the knowledge to achieve a successful end.
"We didn't know enough and we still don't know enough," he said. "Most of us - me included - had a very superficial understanding of the situation and history, and we had a frighteningly simplistic view of recent history, the last 50 years," he said.
The most difficult task, the General says, will be to create a legitimate government that ordinary Afghans could believe in and that would balance the influence of the Taliban.
According to the BBC, more than 2,500 international troops have been killed in the decade the war has been going on - most of them American and the conflict has already surpassed Vietnam to become the longest war in US history.
It says Western officials admit that parts of the country will remain violent after 2014 when Nato relinquishes its combat role and, without a peace deal with the Taliban, few expect the war to be brought to an end.