Book excerpt: This book examines the regional order in the Gulf Region and the wider Middle East, focusing on regional rivalries and security alliances. The authors analyze the regional system in terms of its general structure as well as the major inter-state and non-state security alliances. The structure of the regional system in the wider Middle East and the shake-ups it has experienced explain the ongoing regional rivalry and polarization since 2011 in hotspots such as Syria, Yemen, and Libya. As such, the various chapters address regional transition and power dynamics between and among regional great powers and non-state militant actors across the Gulf Region and the wider Middle East in terms of the alliance building, persistence, and disintegration since 2011.