In a primeval and prehistoric world the first fuel was wood. Wood is basic and primary, and it's comforting. Early man learned to tame fire some time between 72,000 to 164,000 years ago,http://coyoteprime-runningcauseicantfly.blogspot.com/2009/08/archaeology-early-man-used-fire-72000.html depending on your archeological source.
Early people used fire for warmth and for light to save themselves from others animals. That was a big step - humans graduated from being dinner, to cooking it. They fired up the wood, put stones on the fire, and meat on the stones. Read: "Catching Fire," by Richard Wrangham. For thousands of years, wood was the primary fuel of humans. Wood is basic; wood is good.
Most countries in the world began to also use oil, and then coal, natural gas, then electricity, but Afghanistan was/is still dependent upon wood for fuel.
The real problem with wood is that 70% of Afghanistan is deforested - in an already arid land, trees are cut down and/or damaged from years of war, and not replanted. The extinction of wood is eminent.
On the roads of Afghanistan, other than military vehicles, most trucks carry huge loads of wood piled 12 feet high above the sides of the trucks - freshly chopped wood coming in from the countryside into towns; the most common sight on streets and highways is trucks of wood. http://www.spacedaily.com/reports/The_Lost_Forests_Of_Afghanistan_999.html
In the past, the people of Afghanistan were always hearty, robust survivors under sometimes extreme conditions. I have a mental picture of 2000 soldiers in the army of Alexander the Great, frozen in place, solid, in fighting position, dead, from an quick and extreme freeze, while the local people knew how to dig in and adapt, much like today.