In the Soviet army it takes more courage to retreat than advance.
If there's ever an example that military power alone cannot be successful in Afghanistan I think it was the Soviet experience.
Those who remember Washington's cold war culture in the 1980s will recall the shocked reactions to Reagan's intervention. People interested in foreign policy were astonished when in 1985 he met alone at Geneva - alone not a single strategic thinker at his elbow! - with the Soviet Communist master Gorbachev.
Look at the Afghans during the time of the Soviet invasion. They were among the poorest Muslims in the world yet they were sustained by their faith in God and God alone.