Eighty-seven years ago, my grandfather stopped being a German citizen. This February, I became one. It was 1935, and he was living in France when the Reich Citizenship Law passed in Germany. It was part of the Nuremberg Laws under Hitler’s Nazi regime, and it specified that Jews were not of the German race—and therefore no longer citizens. My grandfather, Kurt, was Jewish. There must have been a moment when, one day without warning, my grandfather received the news that he was no longer a German citizen. Nearly a century later, one day without warning, the granddaughter he had never...