This study examines the foreign policy and national security implications of a single dominant hypothesis: that a dangerous world may lie ahead, a world of greater turbulence than today's. Surveying the many negative trends occurring just a few years after the end of the Cold War, it postulates that a world worse than today's--a dangerous world--could evolve, requiring that current national security policy and defense strategy be altered. Proposing a process in which the United States must think deeply about exactly what confronts it, what options it has, and what it is trying to achieve, the study seeks first to conceptualize such a world. It begins by reviewing the optimistic literature that came out just after the Cold War ended and analyzing its fallacies, then scrutinizes the more recent realism-based pessimistic literature that describes features of a global system emerging from the negative trends. Given what seems most plausible in the literature, the study proposes a scenario with three main aspects: political and economic tension in three primary regions--Asia, the Middle East/Persian Gulf, and Europe--geopolitical relations of the West with Russia and China, and tenuous Western Alliance cohesion. It examines the interrelationships of all three aspects and postulates U.S. policy for a new global alliance for security and prosperity to handle those aspects of a dangerous future. The policy emphasizes domestic economic recovery, protects U.S. interests and allies, advances democratic values, and pursues global stability. The policy would be a flexible creation rather than a fixed blueprint. The study further analyzes the five regions of the scenario to identify military imbalances that could contribute to destabilization and a dangerous world. It then proposes a military strategy that would be similarly flexible, balancing competing concerns and embracing the different relationship that will exist between war and politics. In a dangerous world in which it will be difficult to plan where a contingency will occur, force planning will emphasize the ability to perform generic missions ranging from peacetime stability to regional nuclear conflicts.