A retired foreign service officer, Lorenz explores the prospects for a strengthened U.N. collective-security system to tackle the changing nature of regional and global threats. He acknowledges in his opening historical survey the stubborn constraint on collective security: the reluctance of major states to participate under the leadership of others in places where vital interests are not at stake. But he goes on to argue that the nature of post-Cold War conflict gives the United Nations a chance to organize forces capable of deterrence and rapid intervention in cases of regional aggression. One interesting proposal suggests a mobile international deterrent force sponsored by coalitions of concerned states. In contrast to the U.N. Charter, which envisages a force to stop great-power aggression, this plan addresses the post-Cold War need for quick-response deterrent forces that are regionally organized -- a modest idea but one worthy of debate. More problematic is that its success still hinges on the willingness of the United States and the other major powers to commit in advance to the use of force even when their reluctant citizens see no compelling national interests. In the face of this skepticism, it is unlikely that Lorenz will make much headway.