This volume of the Future of Warfare series explains six geopolitical trends--U.S. polarization and retrenchment, China's rise, Asia's realignment, emergence of a revanchist Russia, upheaval in Europe, and turmoil in the Islamic world--that will drive conflict between now and 2030. These trends will shift U.S. alliances; pull limited resources in different directions; and, ultimately, create a deepening strategic dilemma for U.S. defense strategy.