This book develops a theoretical and empirical argument about the disintegration of security communities, and the subsequent breakdown of stable peace among nations, through a process of norm degeneration. It draws together two key bodies of contemporary IR literature – norms and security communities – and brings their combined insights to bear on the empirical phenomenon of disintegration. The investigation of normative change in IR is becoming increasingly popular. Most studies, however, focus on its progressive connotation. The possibility of a weakening or even disappearance of an established peaceful normative order, by contrast, tends to be often either neglected or implicitly assumed. Normative Change and Security Community Disintegration: Undoing Peace advances the contemporary body of research on the important role of norms and ideas by analytically extending recent Constructivist arguments about international norm degeneration to the regional level and by applying them to a particular type of regional order – a security community.