Among conflict researchers there is a growing consensus that the “classical” state-centric conception of war can no longer grasp a large number of armed conflicts. Departing from this observation, we have developed a broadened typology of war which proceeds from the political status of the protagonists and from territorial expansion. As a result, we categorized four types of war: 1. inter-state wars (between at least two sovereign states), 2. extra-state wars (between a state and one or more non-state groups outside its territorial boundaries), 3. intra-state wars (between a government and one or more non-state parties within the boundaries of an internationally recognized state), and 4. sub-state wars (between mostly non-state actors within or across borders). The proposed integration of a sub-state war category reflects the debate about the changing patterns of warfare in the post-Second World War period and follows the underlying rule that a classification of war is best arranged according to the political status of the protagonists. In consequence, wars between private armed groups can be made accessible for both empirical and systematic analyses (concerning their occurrence, duration, and correlates) and for comparative purposes (in relation, for example, to intra-state and inter-state wars).