Maajid Nawaz spent his teenage years listening to American hip-hop and learning about the radical Islamist movement spreading throughout Europe and Asia in the 1980s and 90s. At 16, he was already a ranking member in Hizb ut-Tahrir, a London-based Islamist group. He quickly rose through the ranks to become a top recruiter, a charismatic spokesman for the cause of uniting Islam's political power across the world. Nawaz was setting up satellite groups...