Two books by Vejas G. Liulevicius might be of use here. The German Myth of the East: 1800 to the Present is an intellectual history of the mentalities behind the drang nach Osten. More directly related to the issues of paramilitaries and violence is Liulevicius's War Land on the Eastern Front: Culture, National Identity, and German Occupation in World War I which has chapters on the postwar chaos and draws linkages between the Freikorps and Ober-Ost's policies. Annemarie Sammartino's The Impossible Border: Germany and the East, 1914-1922 is an intellectual history on German visions of a Baltic empire like The German Myth of the East, but more focused on the earlier part of the twentieth century than the former book. Mark Jones has a new study on violence in the Weimar Republic, Founding Weimar: Violence and the German Revolution of 1918–1919 that is more focused on their actions within Germany. Robert Gerwarth's The Vanquished: Why the First World War Failed to End is an OK survey of paramilitary other violence. Gerwarth's text is decent for German affairs, but the book's coverage of areas outside his expertise is spotty (the sections on Ireland are not very good) and the book suffers from trying to fit all these diverse movements into a singular paradigm. Gerwarth was also the editor of a decent anthology on paramilitaries after WWI, War in Peace: Paramilitary Violence in Europe After the Great War.