Steven David makes a powerful case that civil wars, rather than traditional international conflicts, are now the most likely source of serious threats to American interests. David's analysis of the probable causes and potential consequences of major unrest in four key countries is persuasive and sobering, as are his conclusions: lacking reliable means to prevent such conflicts, the best we can do is to prepare for their consequences. This provocative and original study should be read by policy makers as well as scholars. - Aaron Friedberg, Princeton University