Does the proliferation of security communities around the world presage a new era of competition between regions or an era of intensified global integration? This important new study assesses the relationship between security communities and their neighbours and asks whether processes of regional integration will contribute to a global 'clash of civilizations'. The first part of the book builds a framework for assessing the changing relationship between a security community and its neighbours, looking at the ideas and physical relations that bind the community together and the extent to which these ideas and networks cross the boundary between members and non-members. Drawing on four detailed case studies (Western Europe, Southeast Asia, the Persian Gulf and North America), Alex J. Bellamy argues that the more mature a security community becomes, the less likely it is to become a 'regional fortress'. As communities mature, its members begin to adopt cooperative approaches to security as both insiders and outsiders are socialized into new patterns of behaviour.