Many years ago, in the 1980s, I went to Brighton Beach, then in its heyday as a district of newly arrived Soviet Jews. It was a grand event, rich in humor and tinged with nostalgia. I asked a middle-aged partygoer for his thoughts on his lost homeland, and his reply has stayed with me: “I hate Russia, for forcing me to leave her.” It was an apt summary of what waves of émigrés from Russia and the Soviet Union since the early 20th century have felt: a sorrowful sense of loss for a motherland — what Russians call “toska po...