No one knows how Kamran Hasan became a militant. The history-loving 23-year-old had returned home from Islamabad, where he worked as a chartered accountant, and had his hopes set on a degree in education. But then in June, he disappeared. A brief phone call to his father came days later. “He told me, ‘I am going to the mountains,’” says his father, Mohammad Akram, who knew that meant only one thing: his son was joining the militant insurgency that had rocked their home region of Balochistan for decades. “I begged him no, asked if it was reasons of money or...