For a generation, relations between the United States and Russia were essentially about history. Since the Cold War's end, Russia had become increasingly peripheral to the U.S. and much of the rest of the world, its international importance and power seemingly consigned to the past. That era has now ended.

To be sure, the current conflict between the U.S. and Russia over Ukraine is a mismatch, given the disparity in power between the two sides. Russia is not, and cannot even pretend to be, a contender for world domination. Unlike the Soviet Union, it is not driven by some universal ideology, does not lead a bloc of states ruled by the same ideology, and has few formal allies (all of which are small). Yet the U.S.-Russia conflict matters to the rest of the world.

It obviously matters most to Ukraine, part of which has become a battlefield. The future of Europe's largest country — its shape, political order, and foreign relations — depends very much on how the U.S.-Russian struggle plays out.