The Cold War ended with an exhilarating wave of events: the toppling of the Berlin Wall, the rise of the dissident poet Vaclav Havel, the revolution in Romania. Americans rejoiced at the dramatic conclusion of the long struggle. "But victories in wars--hot or cold--tend to unfocus the mind," writes John Gaddis. "It can be a dangerous thing to have achieved one's objectives, because one then has to decide what to do next." In The United States and...