'A colossal failure,' says former UN envoy Peter Galbraith

Galbraith said rampant corruption within the police and all levels of government meant that money that the U.S. was giving in aid often ended up in Taliban hands, as local warlords, police and government officials cooperated with the insurgent group.

Under Taliban rule between 1996 and 2001, women could not work, girls were not allowed to attend school and women had to cover their faces and be accompanied by a male relative if they wanted to venture out of their homes.

Much has changed in the two decades after they were overthrown by a U.S.-led invasion and Galbraith expressed concern about the future of women, girls and the Hazaras minority group.

"In the last 20 years, Afghanistan's become a place transformed, a much more modern South Asian country and particularly Kabul which has quadrupled in size and has tall buildings and all of that. So how people in Afghanistan and particularly in Kabul are going to adjust to this new era, it's going to be really, really difficult."