US Commander in Afghanistan reflects on American's longest war ahead of September 11 20th anniversary

Next week America and the world will mark 20 years since the September 11 terror attacks, which triggered the war in Afghanistan.

As military and political leaders face the fall out from the disastrous end to the conflict, those who served are left wondering what lessons will be learned and, if it was all worth it.

Colonel Robert Campbell served two tours as a US Commander in Afghanistan and, like many veterans, he's still trying to make sense of the pitiful collapse of the Afghan government and security forces.

"There was never that national will and we were trying to speed it a long too quickly, these things take decades," Colonel Campbell told 9News.

Between 2009 and 2015 Colonel Campbell worked alongside Afghan leaders and he now believes building a conventional military in America's image was a mistake.

"We had built these beautiful bases for the military, we had equipped them with equipment that would be hard for us to maintain and operate, it was that technically advanced.

"And they were losing the war, because they would sit on these bases while the Taliban won the day in the villages."

"My fear is that this fades from the American and Australian consciousness when it goes out of the headlines and you've got everybody out of there."

Now, there's a new era in American foreign policy and the return of an old era for the Afghan people.

Still, Colonel Campbell believes the past twenty years have left the country a better place.

"You can't unlearn things... you cant unsee things, and 20 years of what we did especially for women's rights, giving them a chance to get an education and flourish and grow, they have seen that now and you can't shut that off, and that all came from service members from your country and mine."

"I remain proud of my service there and the service of all the Australians I served with and nothing will change that."