Daniel Siemens is Professor of European History at Newcastle University and the author of Stormtroopers: A New History of Hitler’s Brownshirts. Whenever we witness paramilitary or excessive violence by state authorities, comparisons with National Socialism – Nazism – quickly come to mind. Beyond what students learn in school, and thanks to films, books and increasingly computer games, we are more comprehensively informed about the Third Reich than about almost any other period in recent history. On the political left, historical comparisons with Nazism often serve to portray current events in a particularly negative light and as early warning signs of...