For the "western" troops to leave Afghanistan without letting it continue to fall deeper into its the civil war a political solution will be required. Such a solution will have to include a government participation for the Taliban.

Washington is not yet willing to allow that. That has nothing to do with some moral question or women rights. Washington has lots of friends and allies who behave much worse then the Taliban ever did. The real issue is a, largely imagined, U.S. conflict with China.

To negotiate seriously with the Taliban an agreement will have to be found with the Pakistani military which at least partly controls that movement.

The concern of the Pakistani military is an Afghanistan under heavy Indian influence and, resulting from that, a potential two front war. The concern is not without merit. Karzai was educated in India and India has same para-militaries, an embassy and four consular offices in Afghanistan which certainly do not have the sole purpose of stamping visa into passports.

For Pakistan to agree to further serious negotiations with the Taliban, at least a temporary solution has to be found to alleviate its fears with regard to India.

The way to fundamentally relieve Pakistani fear of India is to find a solution for Kashmir. While the Kashmir conflict is partly a Hindu versus Muslim religious conflict and partly an ethnic/tribal conflict the real Kashmir concern for Pakistan are the water sources from the Himalaya that spring up in Kashmir and feed the Indus river. The Indus is literally the lifeline that feeds Pakistan's people. Uncontested Indian rule in Kashmir with the ability to cut off Pakistan's water is a knife to its throat.

A solution for Kashmir could be some vote for independence by the people living there, as promised to them a long time ago but never allowed, followed by a neutrality and water sharing agreement with its neighbors.

To at least temporarily have the Pakistani agree on a negotiated solution for Afghanistan, India (and Karzai) will have to leave Afghanistan. The U.S. would have to press India for this to happen.

But the U.S. does not want to pressure India on anything, not even on leaving Afghanistan. It is fantasizing about a big conflict with China in which, it assumes, India will be an ally.

So for now the U.S. will continue to pay a $120 billion per year in Afghanistan to achieve nothing. A few years down the road and after some more serious budget pressure Congress will finally have enough of it. The U.S. will then leave without a political solution. The civil war in Afghanistan will continue and a few years later the Taliban will have again won.

That is not the necessary outcome, but it is what the current purely military U.S. policy, if continued, will achieve.

Recommended readings:
How the Afghan Counterinsurgency Threatens Pakistan – Anatol Lieven/The Nation
The Way Out of Afghanistan – Ahmed Rashid/NYRB
In deadly Kandahar, skepticism over gains cited in Afghan war review – CSM
Fresh Approach: It’s Time for the Afghans to Leave Afghanistan – World Affairs