Possibly the most fashionable theme in current discussions of the future is whether China will replace the United States as the leading world power. That it will do so seems to be taken for granted in pop-historical circles, as well as among economic forecasters or futurists (who currently have a record that does not inspire confidence). A Goldman Sachs analysis declares that China will replace the United States as the largest economy in the world by 2027. But the largest economy is not automatically the leading nation. And ruling the world is more of a problem than one thinks, as Washington is discovering.