Book excerpt: The Great Power Peace has tenuously held since the end of World War II. However, it now appears on shakier ground than ever before. For the first time since the end of the Cold War, the official National Security Strategy of the United States declared that “the risk of conflict between major powers is increasing.” Undoubtedly, such a conflict would cause unprecedented human, environmental, and economic damage. As noted by Ronald Reagan and Mikhail Gorbachev in 1985—and reiterated by Joe Biden and Vladimir Putin in 2021—“a nuclear war cannot be won and must never be fought.” While a clear sentiment, how to ratchet tensions down and sustainably coexist is considerably less clear. Moreover, the need for international cooperation to address issues such as climate change, artificial intelligence, and future pandemics is greater than ever.