As we grapple with the problems and perils of the 21st century, the great debates of the 20th have not gone away. Some of the most contentious questions have to do with the history of Communism, whose unholy ghost continues to haunt us more than a decade after the demise of the Soviet Union. Was Communism as evil as Nazism? Did the Western left collude in its evil? These issues are powerfully confronted by the British novelist Martin Amis in his new book Koba the Dread: Laughter and the Twenty Million. Koba was a nickname for Stalin, and the...