Epic songs and battle hymns have for centuries lent fortitude to tribal warriors. But as international forces begin winding down their operations, the Islamist militants are redoubling efforts to take ownership of this treasured cultural tradition and use it for their own ends. They believe poetry converted to chants will help them recruit new fighters and inspire existing ones. Earlier this year the Taliban launched a new website called Tarani (meaning chants or ballads). It provides links to hundreds of chants by dozens of different singers. A book of Taliban poems has even been translated into English and published this...