How could the Nazis have committed the crimes they did? Why did commandants of concentration and death camps willingly - often enthusiastically - oversee mass murder? How could ordinary Germans have tolerated the removal of the Jews? In this book, Laurence Rees combines history and the latest research in psychology to help answer some of the most perplexing questions surrounding the Second World War and the Holocaust. Ultimately, he delves into the darkness to explain how and why these people were capable of committing the worst crime in the history of the world. Rees traces the rise and eventual fall of the Nazis through the lens of 'twelve warnings' - whilst also highlighting signs to look out for in present day leaders who, for example, take control of the media, propound conspiracy theories, and talk about 'them' against 'us'.