If a country, a nation is to become one, achieve unity it needs a centre. Afghanistan, has in its history never really had national unity, it was an empire dominated by Paytans since its conception in 1770.
After the northern tribes, represented by a bunch of warlords together with the CIA and the USAF defeated the Taliban a tribal head named Karzai was made President of Afghanistan.
But Karzai does not have a power base. In the struggle between the Taliban and the pro-western Afghan "government" the only real power are the Taliban. This is brought out by a fragment of a long article on Karzai in the New York Times by Elisabeth Rubin. At some point Kabul is rocked by 6 hours of riots against foreigners and the U.S. Forces there and an abservers is quoted to say:
I felt really bad for him,” Jawed Ludin recalled. Karzai was so alone. He continued to watch the riot footage in his back room, trying to glean the plot. “I realized that, at that time, he had no dependable instrument of power,” Ludin said. “He didn’t have the money, the police, the intelligence. He had nothing.Things fall apart.
And this in a nutshell is why the pro-western alliance in Afghanistan will fail.