There is, in theory, a plausible role for the European Union as the partner of a militarily assertive United States: the peacekeeper that follows in the wake of the peacemaker. The war in Iraq, however, has raised the possibility of a diametrically different role for Europe: as a potential imperial rival to the United States. There is no need to invoke the memory of either Rome or Byzantium to make the case that Europe is capable of spoiling America’s unipolar party. The successful conclusion of accession agreements with ten new member countries – not to mention the sustained appreciation of the euro against the dollar since Kennedy’s article appeared – have seemingly vindicated this analysis. So too, in the eyes of some commentators, has the vociferous and not wholly ineffectual opposition of at least some E.U. member states to American policy in Iraq. If the U.S. has an imperial rival today, then the E.U. appears to be it.