This book uses Boko Haram as a case study to delve into the operations of extremist groups in sub-Saharan Africa, with a particular focus on the unique cultural contexts in which they function. The book explores how such groups navigate ethnically diverse environments and manage to forge a sense of collective homogeneity, even in the face of internal diversity. Drawing from first-hand interviews with ex-fighters and a thorough examination of the group's operational dynamics—including recruitment, indoctrination, combat leadership, and unit behaviour—the book identifies moments when, despite Boko Haram's aim to transcend ethnic boundaries, ethnicity nonetheless becomes a defining factor within specific combatant units. It develops a theoretical framework to explain these instances, building on and extending existing socialisation theories to understand when and why socialisation processes fail, ultimately causing ethnicity to resurface within these units. By exploring how tribal and ethnic considerations influence the group's functioning, this book provides a more nuanced understanding of contemporary insurgent groups and the social forces that shape them. This book will be of much interest to students of political violence, African politics, and security studies.