Afghanistan’s master guerrilla commander, Ahmed Shah Massoud, was assassinated by suspected al-Qaeda suicide bombers just two days before September 11. But his Northern Alliance coalition became the U.S.’s most important weapon against the Taliban in a war that combined 19th-century slaughter and 21st-century technology. As alliance soldiers marched on Kabul—with a massed-infantry assault amid the deadly shadows of B-52 bombers—the author saw Massoud’s legacy revealed, in the Afghans’ hatred of foreigners fighting for the Taliban, in their readiness to die for freedom, and even, poignantly, in one man’s act of mercy.