Introduction xi As we authored this book, the United States faces unprecedented chal- lenges around the globe. An increasingly assertive China flexes its muscles in the South China Sea and toward Taiwan while exerting its growing eco- nomic might internationally through the Belt and Road Initiative and the Global Development Initiative. Russia continues to put pressure on both U.S. allies in NATO and partners in Europe, while demonstrating its own ability to challenge U.S. leadership, whether in the Arctic, the Caucasus region, or in the Middle East. Smaller states, such as Iran and North Korea, continue to flout international rules underpinned by U.S. leadership and power. In addition, challenges such as COVID, climate change, migration, democratic backsliding, and pervasive economic imbalances weaken the power of not only the United States but also those allies and partners who share the same values and interests as the United States. While it will be impossible to return to the very brief unipolar moment at the end of the Cold War, the insights contained in this book can help guide policymakers and warfighters as they confront the challenges ahead to U.S. leadership and enable them to sustain America’s strategic advantage.