Horse soldiers - Doug Stanton

The Horse Soldiers is the true, dramatic account of a small band of Special Forces soldiers who entered Afghanistan immediately following September 11, 2001 and, riding to war on horses, defeated the Taliban. Outnumbered 40 to 1, they capture the strategic Afghan city of Mazar-e Sharif, and thereby effectively defeat the Taliban throughout the rest of the country. They are welcomed as liberators as they ride on horses into the city, the streets thronged with Afghans overjoyed that the Taliban have been kicked out.
The soldiers rest easy, as they feel they have accomplished their mission. And then, the action takes a wholly unexpected turn. During a surrender of Taliban troops, the Horse Soldiers are ambushed by the would-be P.O.W.s and, still dangerously outnumbered, they must fight for their lives in the city's ancient fortress known as Qala-I Janghi, or the House of War . . .