This book examines the legitimation practices of Presidents Bush and Obama in the transformation of detention norms in the war on terror. The focus is on the conflict between the US use of force and the commitment to protective norms of legitimate force. The central question is how both presidents used legitimation to justify normative changes in detention law, especially indefinite detention. The study analyzes strategic legitimation activities in the security policy discourse in which norms of legitimate violence shift from containing it to enabling it. The approach combines IR norms research and international law with a pragmatic-abductive method. Using case studies, event analysis and speeches, it examines how Bush and Obama used legalization and justification strategies to transform norms in the Guantanamo case. The resulting patterns lead to a concept of strategic practices of legitimation to justify violence in breach with international law.