Book excerpt: This book examines changes in the Persian Gulf security complex following the United States (US) invasion of Iraq in 2003, focusing on threats to the collective identities of two religious sects - Shia and Sunni. Although there is a growing body of literature examining security in the Persian Gulf, little focus has been given to the theoretical and methodological aspects of the problem. In this volume, Shayan analyses the causes behind the security changes which occurred in the region since 2003 and demonstrates how regional security dynamics are interlinked to perceived sectarian threats on the Shia and Sunni religious identities. This text is essential reading for political scientists, policy makers and scholars of international relations.