Nestled amid the green Crimean hills, lapped by the Black Sea’s languid waves, Yalta’s battle-scarred appearance in February 1945 prompted Winston Churchill to call it “the Riviera of Hades.” It still has the faint aura of a seaside resort for secret policemen.

Today, of course, the Soviet system is a (slowly) fading memory, and the organizers of this year’s Yalta European Strategy conference could even make fun of Stalin in a specially commissioned cartoon. Yet Stalin’s ghost is not so easily exorcised. Although nearly 70 years have passed since President Franklin D. Roosevelt and a reluctant Churchill handed Eastern Europe over to the Soviet dictator, the old ogre still seems to haunt the Livadia Palace.

After President Barack Obama’s fumbling over Syria, Russia is once again flexing its muscles — not just in the Middle East, where President Vladimir Putin is bidding for the role of power broker, but also in his own backyard. At Yalta in 1945 it was above all the fate of Poland that was at stake; this year it was the turn of Ukraine itself....