A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission (fission bomb) or a combination of fission and fusion (thermonuclear weapon). Both reactions release vast quantities of energy from relatively small amounts of matter. The first fission ("atomic") bomb test released the same amount of energy as approximately 20,000 tons of TNT (see Trinity (nuclear test)). The first thermonuclear ("hydrogen") bomb test released the same amount of energy as approximately 10,000,000 tons of TNT. Nuclear weapons, as the most destructive instruments ever invented, had a stabilizing effect on superpower relations by making any conflict unacceptably costly. However, geopolitical change and the evolution of military technology suggest that the composition of our nuclear forces and our strategy for their employment may be different in the twenty-first century. The time is right for a fundamental rethinking of our expectations and requirements for these unique weapons. This book argues that nuclear weapons have destabilized the subcontinent, principally because of their interaction with India and Pakistan's territorial preferences and relative military capabilities. These findings challenge both optimistic and pessimistic conventional wisdom and have implications beyond the World.