The book explores the ways in which social cohesion -- measured as trust in unknown fellow citizens -- can be established and undermined. It examines the US and UK, where social cohesion declined in the latter part of the twentieth century, and Sweden and Denmark, where social cohesion increased, and aims to put forward a social constructivist explanation for this shift. Demonstrating the importance of public perceptions about living in a meritocratic middle class society, the book argues that trust declined because the Americans and British came to believe that most other citizens belong to an untrustworthy, undeserving, and even dangerous 'bottom' of society rather than to the trustworthy middle classes. In contrast, trust increased amongst Swedes and Danes as they believed that most citizens belong to the 'middle' of society rather than to the 'bottom'. Furthermore, the Swedes and Danes came to view the (perceived) narrow 'bottom' of their society as trustworthy, deserving, and peaceful. The book argues that social cohesion is primarily a cognitive phenomenon, in contrast to previous research, which has emphasized the presence of shared moral norms, fair institutions, networks, engagement in civil society etc. The book is based on unique empirical data material, where American survey items have been replicated in the British Social Attitude survey and the Danish and Swedish ISSP surveys (exclusively for this book). It also includes a unique cross-national study of media content covering a five year period in UK, Sweden, and Denmark. It demonstrates how 'the bottom' and 'the middle' is differently constructed across countries.