In the 1950s, '60s and '70s, security experts worried about the spread of nuclear weapons. Now, after decades of academic analysis, some argue that nuclear weapons in more hands may be better. During the 2016 presidential campaign, Donald Trump suggested the United States might be better off if Japan and South Korea got the bomb. All this raises the question: Should we let the bomb spread? The authors in this volume present a variety of views. Some...