Does the proliferation of nuclear weapons cause ongoing conflicts to diminish or to intensify? The spread of nuclear weapons to South Asia offers an opportunity to investigate this crucial question. Optimistic scholars argue that by threatening to raise the cost of war astronomically, nuclear weapons make armed conflict in South Asia extremely unlikely. Pessimistic scholars maintain that nuclear weapons make the subcontinent war-prone, because of technological, political, and organizational problems. 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 South Asia.