A great deal of interest surrounds the question of how the United States might stack up against a rising China in a great power conflict. Ditto what the best defense strategy, doctrine, and investments militaries need to win a future war. Zack Cooper's Tides of Fortune: The Rise and Decline of Great Militaries tackles both puzzles admirably.

The book advances a simple thesis intuitive even to nonscholars: Great powers (and even perhaps smaller states, as the author later hints) alter their defense policies as they rise and decline. Specifically, states adjust their ends, ways, and means—or objectives, strategies, and investments—based on their perceived relative power. Weaker states perceived as rising will take on more ambitious objectives, offensive capabilities, and sustainable investments (think pre-World War I Germany), whereas declining powers will consolidate their holdings, adapt defensive (or denial) strategies, and invest in expendable assets. Think late Brezhnev-era Soviet Union (I am simplifying the theory somewhat because the author differentiates between weak and strong powers, thereby creating four phases of a state's perceived relative power).

The setup is a long windup to address the book's motivating puzzle (a lede buried in its final chapters): What explains China's recent military shift? Why is