Many scenarios of conflict in the global south are economically driven but have experienced such extreme forms of violence that commentators have reviewed the law of non-international armed conflict (NIAC) in light of the ‘war on drugs’ in several countries of Latin America, and elsewhere. The article also addresses this issue but with a view to better understand the relationship between law and violence. International humanitarian law (IHL) is not understood here as a mere set of neutral normative hypotheses which may or not apply to factual situations, but rather as an important means through which war is constructed. This relationship is reviewed in the framework of the struggle of the Mexican government against powerful drug cartels as well as among the latter, in particular during the administration of President Calderón, from 2006 to 2012. It does so, by analysing the legal narratives that have structured the discourse about Mexico’s violence. By simplifying its complexity, these narratives facilitate the qualification of the situation as internal war. This is contestable as a matter of lex lata. Moreover, it is counterproductive as it reinforces the strategic shifts between the law of war and the law of peace. The article concludes by arguing that the acknowledgment of the complexities of these conflicts is of the utmost importance for IHL, since they put into light the contingent character of some of its structuring categories. This sounds self-defeating but it is necessary for avoiding that this body of law reinforces what it seeks to contain.