In November 1944, a young American soldier wrote back to his parents in the Washington Heights neighborhood of Manhattan. Six years earlier, he and his family had fled Germany for the United States, only weeks before Kristallnacht, the infamous Night of Broken Glass.Now here he was, having returned to the place where, had they stayed, he and his family may well have already perished. "So I am back where I wanted to be," the young man wrote. "I think of the cruelty and barbarism those people out there in the ruins showed when they were on top. And then I...