Despite a quasi-universal recognition of an association between civil war and atrocity, there is surprising little in the way of specified links between the two. Exactly why is civil war associated with excessive violence? Put otherwise, what are the sources of barbarism in civil war? Answering this question is a prerequisite for the formulation of a theory of violence in civil war.

In this chapter, I reconstruct, specify, and contrast four general arguments inspired by different theoretical traditions. The first thesis, present in many historical and descriptive accounts, flows from Thomas Hobbes's insight linking the breakdown of political order to violence. The second, transgression, points to domestic armed challenge as being transgressive of established norms, thus triggering violence. The third account, polarization, can be found in historical and sociological research and stresses deep ideological or social divisions, highlighting the predictably violent effects of what Carl Schmitt described as total enmity. The last thesis stresses violent responses triggered by security concerns related to the technology of warfare practiced in civil wars. I review several theoretical and empirical facets of these arguments and select the last thesis as the most appropriate theoretical foundation for a theory of violence in civil war.