Lies, ego, hubris and self-deception: US experts are counting up the reasons for failure in the two-decade US war in Afghanistan, calling it ill-fated from the beginning, comparable to the American experience in Vietnam.

On Thursday the official US watchdog on operations in Afghanistan said it is too early to call the war a complete failure, because the government retains a slim chance of prevailing over the Taliban, the hardline Islamists that the US and allies ejected from power in November 2001.

But he said that the US forces, who will depart next month, leave behind a corrupt and unmotivated Afghan security forces and a government that could easily succumb to the insurgents.

The "big question," said John Sopko, the Special Inspector General for Afghanistan Reconstruction, is "after all the money, $86 billion, and 20 years, why did we see such poor results?"

Sopko, whose Congressional mandate was to monitor the effectiveness of the military and development effort, said in a discussion with reporters Thursday that two words describe the US experience.

"One is hubris, that we can somehow take the country that was desolate in 2001, and turn it into a little Norway."

"And the other thing is mendacity. We exaggerated, over exaggerated, our generals did, our ambassadors did, all of our officials did, to Congress and the American people, about 'we're just turning the corner, we're about ready to turn the corner.'"

He said that the US military was fixated on short-term achievements and constantly changed its objectives to look better.

"Every time we went in, the US military changed the goalposts, and made it easier to show success. And then finally, when they couldn't even do that, they classified the assessment tool," he recalled.

Washington, he said, thought "that we would create a strong central government."

"And that was a mistake. ... And if you if you talked to any experts on Afghanistan, they would have said, it was a mistake. The problem is, we didn't listen to any of them."

Afghans saw US as invaders

"There can be little doubt that we lost the war," Carter Malkasian, a former senior Pentagon official who served in Afghanistan for years, wrote in a newly published book.

He said that the Taliban showed more will to fight "invaders," while the people viewed the government as dependent on non-Muslim foreigners.

"The very presence of Americans in Afghanistan trod on a sense of Afghan identity that incorporated national pride, a long history of fighting outsiders and a religious commitment to defend the homeland," Malkasian wrote.

"We believed things were possible in Afghanistan -- defeat of the Taliban or enabling the Afghan government to stand on its own -- that probably were not."

From the very beginning, experts say, corruption in the government and security forces, helped by the massive amounts of money the US poured in, eroded any sense of commitment to Kabul.

Meanwhile, even if they were also disliked and poorly managed, the Taliban were more intensely motivated, by religion and hate for the "infidels."

Sopko said that no one could expect the Afghan forces to fight if their salaries weren't paid, they didn't have food, and their ammunition and the fuel for their vehicles was all stolen by corrupt officials.

"The police and soldiers did not want to put their lives on the line for a government that was corrupt and prone to neglect them," said Malkasian.

Rights abuses

A report this month by Human Rights Watch said from early on atrocities and rights abuses by the Afghan government and US forces undermined the many positive benefits of social and economic development that the Americans brought.

HRW cited "the obliviousness or apathy of US generals about atrocities being committed by Afghan forces, the US military, and CIA units."

The group also said under-reported civilian casualties from US airstrikes, like a 2009 bombing that killed 100 civilians in western Farah province, eroded potential support in the countryside for the Americans.

"In these 20 years, the propensity of the United States to prioritize short-term military gains over the creation of genuinely democratic institutions and the protection of human rights fatally undermined both the US mission and the entire post-2001 state-building effort," HRW said.

'We will do this again'

As it exits, Sopko said the US leaves behind a country still suffering huge power shortages and a large, untrammelled trade in opium and heroin, problems US officials had just "kicked down the road."

"Don't believe what you're told by the generals and ambassadors or people in the administration saying we're never going to do this again. That's exactly what we said after Vietnam," Sopko said.

"Lo and behold we did Iraq. And we did Afghanistan. We will do this again. And we really need to think and learn from the 20 years in Afghanistan."