General who led Obama's 'surge' strategy says even now the military does not have the local knowledge to end the conflict

One of America's most celebrated generals has issued a harsh indictment of his country's campaign in Afghanistan on the 10th anniversary of the invasion to topple the Taliban.

The US began the war with a "frighteningly simplistic" view of Afghanistan, the retired general Stanley McChrystal said, and even now the military lacks sufficient local knowledge to bring the conflict to an end.

The US and Nato are only "50% of the way" towards achieving their goals in Afghanistan, he told the Council on Foreign Relations.

"We didn't know enough and we still don't know enough. 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."

McChrystal led the Obama administration's "surge" strategy that started in 2009 and sent US troop levels in Afghanistan to more than 100,000. Widely acknowledged as a gifted military commander, he was forced to resign last year amid controversy over remarks he made to Rolling Stone magazine.

The 10th anniversary of the war, marked on Friday, has prompted sober reflection in the US about a conflict that has passed Vietnam as the military's longest war.

Just over 2,750 foreign troops have been killed – 28% of them in Helmand – while between 14,000 and 18,000 civilians have died as a result of fighting, according to various estimates.

Yet although the US entered Afghanistan to hunt down Osama bin Laden and topple the Taliban, its most prominent targets quickly slipped across the border into Pakistan.

The al-Qaida leader was discovered in Abbottabad, north of Islamabad, last May, while the Taliban have used remote border bases in Pakistan's tribal areas to launched a stiff resurgence.

In his comments on Thursday night, McChrystal also indirectly criticised the Bush administration's decision to invade Iraq in 2003, saying it made success in Afghanistan more difficult to achieve. The invasion "changed the Muslim world's view of America's effort", he said.

"When we went after the Taliban in Afghanistan in 2001, there was a certain understanding that we had the ability and the right to defend ourselves and the fact that al-Qaida had been harboured by the Taliban was legitimate. I think when we made the decision to go into Iraq that was less legitimate [in the eyes of the Muslim world]."

The 10th anniversary has also been marked in downbeat fashion in Afghanistan where talk of US-driven "nation building" has largely evaporated. Despite $57bn in international aid since 2001, aid agencies say most people remain mired in deep poverty.

"There has been some important progress, especially in urban areas," said Anne Garella of Acbar, an umbrella group of 111 foreign and local aid agencies. "But our research highlights the gap behind positive rhetoric and grim reality."

An Acbar study found that 80% of Afghans now have access to health services compared with 9% in 2001. The number of children in school has rocketed from barely one million a decade ago, 5,000 of them girls, to seven million today, one third of whom are girls.

But Afghanistan still has been some of the world's worst health indicators due to shoddy facilities, conflict and official corruption.

Afghans have grown highly sceptical of western aid over the years, with a widespread perception – partly well founded – that much of the money finds its way back to western countries through security costs and inflated expatriate wages.

But the greatest worry for most Afghans now is the consequence of the US drawdown planned for the end of 2014, which will see the vast majority of 150,000 foreign troops leave the country.

The American plan is to hand power to the shaky Karzai-led government, which is plagued by corruption and enjoys diminishing credibility. McChrystal said that building a legitimate government that ordinary Afghans believed in, and which could serve as a counterweight to the Taliban, was among the greatest challenges facing US forces.

Efforts are under way to bolster the government's authority. Nato says it will have trained 325,000 Afghan soldiers by January 2015, and the US is likely to continue financial support, although exact levels have yet to be decided.

But rising ethnic and political tensions could destabilise the country before then. And plans to bring the Taliban to peace talks were hit by the assassination of Karzai's main peace envoy, Burhanuddin Rabbani, last month.