Modern-day Europeans by the millions proudly trace back their national identities to the Celts, Franks, Gauls, Goths, Huns, or Serbs--or some combination of the various peoples who inhabited, traversed, or pillaged their continent more than a thousand years ago. According to Patrick Geary, this is historical nonsense. The idea that national character is fixed for all time in a simpler, distant past is groundless, he argues in this unflinching reconsideration of European nationhood. Few of the peoples that many Europeans honor as sharing their sense of ''nation'' had comparably homogeneous...