In the early 1970s, after the publication of the now classic sociological studies "Primitive Rebels" and "Bandits" by historian Eric Hobsbawm, hajduks started appearing in western social and anthropological literature. Hobsbawm invented the term "social bandit" to describe outlaws who operate on the edges of rural societies by fighting against authorities and sometimes helping the ordinary people. There has always been a degree of fluidity in their status, whereby, as described by John Koliopoulos in his study of Greek klephts, "Brigands with a Cause", brigands would sometimes change sides and start acting on behalf of the authorities to preserve peace and suppress banditry, and vice versa.