Focusing on the major cases of genocide in twentieth-century Europe, including the Armenian genocide, the Holocaust and genocide in the former Yugoslavia, as well as mass killing in the Soviet Union, this book outlines the internal and external roots of genocide. Internal causes lie in the rise of radical nationalism and the breakdown of old empires, while external causes lie in the experience of mass violence in European colonial empires. Such roots did not make any case of genocide inevitable, but they did create models for mass destruction. This book enables students to assess the interplay.