What kind of nuclear strategy and posture does the United States need to defend itself and its allies? According to conventional wisdom, the answer to this question is straightforward: the United States needs the ability to absorb an enemy nuclear attack and respond with a devastating nuclear counterattack. These arguments are logical and persuasive, but, when compared to the empirical record, they raise an important puzzle. Empirically, we see that the United States has consistently maintained a nuclear posture that is much more robust than a mere second-strike capability. How do we make sense of this contradiction? Scholarly deterrence theory, including Robert Jervis’s seminal book, The Illogic of American Nuclear Strategy, argues that the explanation is simple—policymakers are wrong. This book takes a different approach. Rather than dismiss it as illogical, it explains the logic of American nuclear strategy. It argues that military nuclear advantages above and beyond a secure, second-strike capability can contribute to a state’s national security goals. This is primarily because nuclear advantages reduce a state’s expected cost of nuclear war, increasing its resolve, providing it with coercive bargaining leverage, and enhancing nuclear deterrence. This book provides the first theoretical explanation for why military nuclear advantages translate into geopolitical advantages. In so doing, it resolves one of the most intractable puzzles in international security studies. The book also explains why, in a world of growing dangers, the United States must possess, as President Donald J. Trump declared, a nuclear arsenal “at the top of the pack.”