Europe has been at the center of nearly every great-power competition of the last 500 years, either as home to one or both of the protagonists or as the decisive theater of struggle. No longer: The world wars of the last century saw to that. Yet Europe's nations are still capable of playing a critical role in the defining contest of this century: that between China and America. Or, they can allow the continent to be reduced to a weak, divided region that struggles to make its influence felt.

China desires the latter, and has a strategy for achieving it. The U.S. should prefer an active and capable set of European allies, but its policies have too often played into Beijing's hands.

The world's center of geopolitical gravity has been moving steadily eastward for decades. The Asia-Pacific now significantly outstrips Europe's shares of global GDP and global military spending. And although the rivalry between Russia and the West is significant, the trans-Pacific struggle between China and America is epochal.