Six men sat down for a business meeting on the morning of October 18 last year, amid the hubbub and marble-columned opulence of Moscow’s iconic Metropol Hotel, to discuss plans for a “great alliance.” A century earlier, the grand institution was the scene of events that helped change the face of Europe and the world: Czarist forces fought from inside the hotel as they tried and failed to hold the Bolsheviks back from the Kremlin in 1917, and it was here, in suite 217, that the first Soviet Constitution was drafted after the revolution succeeded. The six men — three...