A great deal of the world's history is the history of empires. Indeed it could be said that all history is colonial history, if one takes a broad enough definition and goes far enough back. And although the great historic imperial systems--the land-based Russian one as well as the seaborne empires of western European powers--have collapsed during the past half century, their legacies shape almost every aspect of life on a global scale. Meanwhile there is fierce argument, and much speculation, about what has replaced the old territorial empires in world politics. Do the United States...