From Putin’s perspective, in other words, the United States hardly looks in retreat. To the contrary, the post-Cold War period has brought one long march by America and its allies closer and closer to the border of Russia itself. But there was no reason to believe that Russia—which under Putin has been regaining its confidence on the world stage—would go on contracting forever. And by 2008, when Russia sent troops into parts of Georgia, it was already clear that NATO’s expansion onto former Soviet soil had come to a halt.

It had stopped for the same reason that General Dwight Eisenhower, determined at the end of World War II to keep the American death toll as low as possible, refused to push into Eastern Europe to prevent the USSR from dominating the region after the war. And for the same reason that President Eisenhower watched Soviet troops crush protests in Budapest in 1956, and President Johnson watched Soviet troops crush the Prague Spring in 1968. The frontiers of American power in Eastern Europe have long been set by Moscow’s willingness to send troops into countries where, by virtue of their geography, Russia is prepared to take casualties and the United States is not. (Just as the limits of Soviet power in the Americas were set in 1962 when John F. Kennedy proved more willing to risk war over Soviet missiles in Cuba than did Nikita Khrushchev.)

To say that the border of Western power has stopped expanding is not to say it has begun to contract.